TAPS AND THREADING DIES

Transcription

1 872 TAPS AN THRAING IS TAPS AN THRAING IS General dimensions and tap markings given in the ASM/ANSI Standard B for straight fluted taps, spiral pointed taps, spiral pointed only taps, spiral fluted taps, fast spiral fluted taps, thread forming taps, pulley taps, nut taps, and pipe taps are shown in the tables on the pages that follow. This Standard also gives the thread limits for taps with cut threads and ground threads. The thread limits for cut thread and ground thread taps for screw threads are given in Tables 3 through 7 and Tables 8a and 8b; thread limits for cut thread and ground thread taps for pipe threads are given in Tables 9a through 10c. Taps recommended for various classes Unified screw threads are given in Tables 11a through 14 in numbered sizes and Table 12 for nuts in fractional sizes. Types Taps. Taps included in ASM/ANSI B are categorized either by the style fluting or by the specific application for which the taps are designed. The following types 1 through 6 are generally short in length, and were originally called Hand Taps but this design is generally used in machine applications. The remaining types have special lengths, which are detailed in the tables. The thread size specifications for these types may be fractional or machine screw inch sizes, or metric sizes. The thread form may be ground or cut (unground) as further defined in each table. Additionally, the cutting chamfer on the thread may be Bottoming (B), Plug (P), or Taper (T). (1) Straight Flute Taps: These taps have straight flutes a number specified as either standard or optional, and are for general purpose applications. (2) Spiral Pointed Taps: These taps have straight flutes and the cutting face the first few threads is ground at an angle to force the chips ahead and prevent clogging in the flutes. (3) Spiral Pointed Only Taps: These taps are made with the spiral point feature only without longitudinal flutes. These taps are especially suitable for tapping thin materials. (4) Spiral Fluted Taps: These taps have right-hand helical flutes with a helix angle 25 to 35 deg. These features are designed to help draw chips from the hole or to bridge a keyway. (5) Fast Spiral Fluted Taps: These taps are similar to spiral fluted taps, except the helix angle is from 45 to 60 deg. (6) Thread Forming Taps: These taps are fluteless except as optionally designed with one or more lubricating grooves. The thread form on the tap is lobed, so that there are a finite number points contacting the work thread form. The tap does not cut, but forms the thread by extrusion. (7) Pulley Taps: These taps have shanks that are extended in length by a standard amount for use where added reach is required. The shank is the same nominal diameter as the thread. (8) Nut Taps: These taps are designed for tapping nuts on a low-production basis. Approximately one-half to three-quarters the threaded portion has a chamfered section, which distributes the cutting over many teeth and facilitates entering the hole to be tapped. The length overall, the length the thread, and the length the shank are appreciably longer than on a regular straight fluted tap. (9) Pipe Taps: These taps are used to produce standard straight or tapered pipe threads. efinitions Tap Terms. The definitions that follow are taken from ANSI/ASM B94.9 but include only the more important terms. Some tap terms are the same as screw thread terms; therefore, see efinitions Screw Threads starting on page Back Taper: A gradual decrease in the diameter the thread form on a tap from the chamfered end the land toward the back, which creates a slight radial relief in the threads. Base Thread: Coincides with the cylindrical or conical surface from which the thread projects.

2 TAPS AN THRAING IS 873 Chamfer: Tapering the threads at the front end each land or chaser a tap by cutting away and relieving the crest the first few teeth to distribute the cutting action over several teeth. Chamfer Angle: Angle formed between the chamfer and the axis the tap measured in an axial plane at the cutting edge. Chamfer Relief Angle: Complement the angle formed between a tangent to the relieved surface at the cutting edge and a radial line to the same point on the cutting edge. Core iameter: iameter a circle which is tangent to the bottom the flutes at a given point on the axis. First Full Thread: First full thread on the cutting edge back the chamfer. It is at this point that rake, hook, and thread elements are measured. Crest Clearance: Radial distance between the root the internal thread and the crest the external thread the coaxially assembled design forms mating threads. Class Thread: esignation the class that determines the specification the size, allowance, and tolerance to which a given threaded product is to be manufactured. It is not applicable to the tools used for threading. Tap Terms Square Sq. Shank Axis Overall Style Shank Thread Lead Angle Thread Chamfer Chamfer Angle Point Core Land Flute xternal Center Internal Center Max. Tap Major Min. Tap Major Basic Major Basic Height Thread Basic Pitch Pitch Tap Crest Basic Crest Angle Thread Flank Basic Minor Base Thread Basic Root Cutting dge Cutting Face No Relief Heel Relieved to Cutting dge Concentric Margin ccentric Relief Negative Rake Angle Concentric Zero Rake Land ccentric Positive Rake Angle Negative Rake Radial Positive Rake Con-ccentric Relief Hook Tangential Measurement Hook Angle (Chordal Measurement)

3 874 TAPS AN THRAING IS Flank Angle: Angle between the individual flank and the perpendicular to the axis the thread, measured in an axial plane. A flank angle a symmetrical thread is commonly termed the half angle thread. Flank Leading: 1) Flank a thread facing toward the chamfered end a threading tool; and 2) The leading flank a thread is the one which, when the thread is about to be assembled with a mating thread, faces the mating thread. Flank Trailing: The trailing flank a thread is the one opposite the leading flank. Flutes: Longitudinal channels formed in a tap to create cutting edges on the thread prile and to provide chip spaces and cutting fluid passages. On a parallel or straight thread tap they may be straight, angular or helical; on a taper thread tap they may be straight, angular or spiral. Flute-Angular: A flute lying in a plane intersecting the tool axis at an angle. Flute-Helical: A flute with uniform axial lead and constant helix in a helical path around the axis a cylindrical tap. Flute-Spiral: A flute with uniform axial lead in a spiral path around the axis a conical tap. Flute Lead Angle: Angle at which a helical or spiral cutting edge at a given point makes with an axial plane through the same point. Flute-Straight: A flute which forms a cutting edge lying in an axial plane. Front Taper: A gradual increase in the diameter the thread form on a tap from the leading end the tool toward the back. Heel: dge the land opposite the cutting edge. Hook Angle: Inclination a concave cutting face, usually specified either as Chordal Hook or Tangential Hook. Hook-Chordal Angle: Angle between the chord passing through the root and crest a thread form at the cutting face, and a radial line through the crest at the cutting edge. Hook-Tangential Angle: Angle between a line tangent to a hook cutting face at the cutting edge and a radial line to the same point. Interrupted Thread Tap: A tap having an odd number lands with alternate teeth in the thread helix removed. In some designs alternate teeth are removed only for a portion the thread length. Land: One the threaded sections between the flutes a tap. Lead: istance a screw thread advances axially in one complete turn. Lead rror: eviation from prescribed limits. Lead eviation: eviation from the basic nominal lead. Progressive Lead eviation: (1) On a straight thread the deviation from a true helix where the thread helix advances uniformly. (2) On a taper thread the deviation from a true spiral where the thread spiral advances uniformly. Thread: The length the thread the tap includes the chamfered threads and the full threads but does not include an external center. It is indicated by the letter B in the illustrations at the heads the tables. Limits: The limits size are the applicable maximum and minimum sizes. Major iameter: On a straight thread the major diameter is that the major cylinder. On a taper thread the major diameter at a given position on the thread axis is that the major cone at that position. Minor iameter: On a straight thread the minor diameter is that the minor cylinder. On a taper thread the minor diameter at a given position on the thread axis is that the minor cone at that position. Pitch iameter (Simple ffective iameter: On a straight thread, the pitch diameter is the diameter the imaginary coaxial cylinder, the surface which would pass through the thread priles at such points as to make the width the groove equal to one-half the basic pitch. On a perfect thread this coincidence occurs at the point where the widths the thread and groove are equal. On a taper thread, the pitch diameter at a given position on the thread axis is the diameter the pitch cone at that position.

4 TAPS AN THRAING IS 875 Point iameter: iameter at the cutting edge the leading end the chamfered section. Rake: Angular relationship the straight cutting face a tooth with respect to a radial line through the crest the tooth at the cutting edge. Positive rake means that the crest the cutting face is angularly ahead the balance the cutting face the tooth. Negative rake means that the crest the cutting face is angularly behind the balance the cutting face the tooth. Zero rake means that the cutting face is directly on a radial line. Relief: Removal metal behind the cutting edge to provide clearance between the part being threaded and the threaded land. Relief-Center: Clearance produced on a portion the tap land by reducing the diameter the entire thread form between cutting edge and heel. Relief-Chamfer: Gradual decrease in land height from cutting edge to heel on the chamfered portion the land on a tap to provide radial clearance for the cutting edge. Relief-Con-eccentric Thread: Radial relief in the thread form starting back a concentric margin. Relief-ouble ccentric Thread: Combination a slight radial relief in the thread form starting at the cutting edge and continuing for a portion the land width, and a greater radial relief for the balance the land. Relief-ccentric Thread: Radial relief in the thread form starting at the cutting edge and continuing to the heel. Relief-Flatted Land: Clearance produced on a portion the tap land by truncating the thread between cutting edge and heel. Relief-Grooved Land: Clearance produced on a tap land by forming a longitudinal groove in the center the land. Relief-Radial: Clearance produced by removal metal from behind the cutting edge. Taps should have the chamfer relieved and should have back taper, but may or may not have relief in the angle and on the major diameter the threads. When the thread angle is relieved, starting at the cutting edge and continuing to the heel, the tap is said to have eccentric relief. If the thread angle is relieved back a concentric margin (usually onethird land width), the tap is said to have con-eccentric relief. -Actual: Measured size an element on an individual part. -Basic: That size from which the limits size are derived by the application allowances and tolerances. -Functional: The functional diameter an external or internal thread is the pitch diameter the enveloping thread perfect pitch, lead and flank angles, having full depth engagement but clear at crests and roots, and a specified length engagement. It may be derived by adding to the pitch diameter in an external thread, or subtracting from the pitch diameter in an internal thread, the cumulative effects deviations from specified prile, including variations in lead and flank angle over a specified length engagement. The effects taper, out--roundness,and surface defects may be positive or negative on either external or internal threads. -Nominal: esignation used for the purpose general identification. Spiral Flute: See Flutes. Spiral Point: Angular fluting in the cutting face the land at the chamfered end. It is formed at an angle with respect to the tap axis opposite hand to that rotation. Its length is usually greater than the chamfer length and its angle with respect to the tap axis is usually made great enough to direct the chips ahead the tap. The tap may or may not have longitudinal flutes. Thread Lead Angle: On a straight thread, the lead angle is the angle made by the helix the thread at the pitch line with a plane perpendicular to the axis. On a taper thread, the lead angle at a given axial position is the angle made by the conical spiral the thread, with the plane perpendicular to the axis, at the pitch line.

5 876 TAPS AN THRAING IS Tap Table 3. ANSI Standard Fraction- Taps Cut Thread Limits ASM/ANSI B NC UNC Threads per Inch Major iameter Pitch iameter NF UNF NS UNS Basic Min. Max. Basic Min. Max All dimensions are given in inches. Lead Tolerance: Plus or minus inch max. per inch thread. Angle Tolerance: Plus or minus 35 min. in half angle or 53 min. in full angle for to thds. per in.; 40 min. half angle and 60 min. full angle for 6 to 9 thds.; 45 min. half angle and 68 min. full angle for 10 to 28 thds.; 60 min. half angle and 90 min. full angle for 30 to 64 thds. per in.

6 Table 4. ANSI Standard Fractional- Taps Ground Thread Limits ASM/ANSI B Threads per Inch Major iameter Pitch iameter Limits Basic H3 & H4 a H4, a H5 b & NC NF NS Pitch H1 Limit H2 Limit Limits H6 c Limits UNC UNF UNS Basic Min. Max. Min. Max. Min. Max. Min. Max. Min. Max b b a a b b a a b b a a b b b b b b b b b b b b b b b b b b b b a a c c a a a a c c a a a a a H4 limit value. b H5 limit value. c H6 li. TAPS AN THRAING IS 877

7 878 TAPS AN THRAING IS Table 5. ANSI Standard Fractional Taps Ground Thread Limits (ASM/ANSI B ) Threads per Inch Major iameter Pitch iameter Limits Basic H4 Limit NC NF NS Pitch UNC UNF UNS Basic Min. Max. Min. Max All dimensions are given in inches. Lead Tolerance: Plus or minus inch within any two threads not farther apart than one inch. Angle Tolerance: Plus or minus 25 min. in half angle for 6 to 9 threads per inch; plus or minus 30 min. in half angle for 10 to 28 threads per inch. For an explanation the significance the H4 limit value range see Standard System Tap Thread Limits and Identification for Unified Inch Screw Threads, Ground Thread starting on page 896. Si ze NC UNC Table 6. ANSI Standard Machine Screw Taps Ground Thread Limits ASM/ANSI B Threads per Inch Major iameter Pitch iameter Limits a NF UNF NS UNS Basic Min. Max. Basic Pitch H1 Limit H2 Limit H3 Limit Min. Max. Min. Max. Min. Max a H7 limits (formerly designated as G) apply to same threads as H3 limits with the exception the and threads. H7 limits have minimum and maximum major diameters inch larger than shown and minimum and maximum pitch diameters inch larger than shown for H3 limits. All dimensions are given in inches. Lead Tolerance: Plus or minus inch within any two threads not farther apart than one inch. Angle Tolerance: Plus or minus 30 min. in half angle for 20 to 80 threads per inch. For an explanation the significance the limit value ranges see Standard System Tap Thread Limits and Identification for Unified Inch Screw Threads, Ground Thread starting on page 896.

8 TAPS AN THRAING IS 879 Table 7. ANSI Standard Machine Screw Taps Cut Threads Limits ASM/ANSI B NC UNC Threads per Inch Major iameter Pitch iameter NF UNF NS UNS Basic Min. Max. Basic Min. Max All dimensions are given in inches. Lead Tolerance: Plus or minus inch per inch thread. Angle Tolerance: Plus or minus 45 min. in half angle and 68 min. in full angle for 20 to 28 threads per inch; plus or minus 60 min. in half angle and 90 min. in full angle for 30 or more threads per inch. Table 8a. ANSI Standard Metric Tap Ground Thread Limits in Inches M Prile ASM/ANSI B Nominal iam, mm Pitch, mm Major iameter (Inches) Pitch iameter (Inches) Basic Min Max Basic Min Max Basic pitch diameter is the same as minimum pitch diameter internal thread, Class 6H as shown in table starting on page Pitch diameter limits are designated in the Standard as 3 for 1.6 to 3 mm diameter sizes, incl.: 4 for 3.5 to 5 mm sizes, incl.; 5 for 6 and 8 mm sizes; 6 for 10 and 12 mm sizes; 7 for 14 to 20 mm sizes, incl.; 8 for 24 mm size; and 9 for 30 and 36 mm sizes. Angle tolerances are plus or minus 30 minutes in half angle for pitches ranging from 0.35 through 2.5 mm, incl. and plus or minus 25 minutes in half angle for pitches ranging from 3 to 4 mm, incl. A maximum deviation plus or minus inch within any two threads not farther apart than one inch is permitted.

9 880 TAPS AN THRAING IS Table 8b. ANSI Standard Metric Tap Ground Thread Limits in Millimeters M Prile ASM/ANSI B Nominal iam, mm Pitch, mm Major iameter (mm) Pitch iameter (mm) Basic Min Max Basic Min Max Basic pitch diameter is the same as minimum pitch diameter internal thread, Class 6H as shown in table starting on page Pitch diameter limits are designated in the Standard as 3 for 1.6 to 3 mm diameter sizes, incl.: 4 for 3.5 to 5 mm sizes, incl.; 5 for 6 and 8 mm sizes; 6 for 10 and 12 mm sizes; 7 for 14 to 20 mm sizes, incl.; 8 for 24 mm size; and 9 for 30 and 36 mm sizes. Angle tolerances are plus or minus 30 minutes in half angle for pitches ranging from 0.35 through 2.5 mm, incl. and plus or minus 25 minutes in half angle for pitches ranging from 3 to 4 mm, incl. A maximum lead deviation plus or minus mm within any two threads not farther apart than 25 mm is permitted. Table 9a. ANSI Standard Taper Pipe Taps Cut Thread Tolerances for NPT and Ground Thread Tolerances for NPT, NPTF, and ANPT ASM/ANSI B Nominal Threads per Inch NPT, NPTF, or ANPT Projection Inches Gage Measurement a Taper per Foot, Inches Tolerance Plus or Minus Cut Thread Ground Thread Cut Thread Ground Thread Min. Max. Min. Max a istance that small end tap projects through L1 taper ring gage (see ANSI B1.20.3). All dimensions are given in inches. Lead Tolerance: Plus or minus inch per inch cut thread and plus or minus inch per inch ground thread. Angle Tolerance: Plus or minus 40 min. in half angle and 60 min. in full angle for 8 cut threads per inch; plus or minus 45 min. in half angle and 68 min. in full angle for to 27 cut threads per inch; plus or minus 25 min. in half angle for 8 ground threads per inch; and plus and minus 30 min. in half angle for to 27 ground threads per inch.

10 TAPS AN THRAING IS 881 Table 9b. ANSI Standard Taper Pipe Thread Widths Flats at Tap Crests and Roots for Cut Thread NPT and Ground Thread NPT, ANPT, and NPTF ASM/ANSI B Threads per Inch Tap Flat Width at Column I NPT Cut and Ground Thread ANPT Ground Thread Minimum a Column II NPTF Cut and Ground Thread Maximum Minimum a Maximum 27 { Major iameter { Minor iameter { Major iameter { Minor iameter { Major iameter { Minor iameter { Major iameter { Minor iameter { Major iameter { Minor iameter a Minimum minor diameter falts are not specified. May be sharp as practicable. All dimensions are given in inches. Note: Cut Thread taps made to Column I are marked NPT but are not recommended for ANPT applications. Ground Thread taps made to Column I are marked NPT and may be used for NPT and ANPT applications. Ground Thread taps made to Column II are marked NPTF and used for ryseal application. Table 10a. ANSI Standard Straight Pipe Taps (NPSF ryseal) Ground Thread Limits ASM/ANSI B Nominal, Inches Threads per Inch a As specified or sharper. Major iameter Min. G Max. H Plug at Gaging Notch Pitch iameter 27 Pitch diameter plug at Actual measured gaging notch pitch diameter All dimensions are given in inches. Lead Tolerance: Plus or minus inch within any two threads not farther apart than one inch. Angle Tolerance: Plus or minus 30 min. in half angle for 14 to 27 threads per inch. Min. K Max. L Minor a Flat, Max Formulas For American ryseal (NPSF) Ground Thread Taps Nominal Major iameter Pitch iameter Max., Inches Min. G Max. H Min. K Max. L Minor 1 16 H K + Q L F M Q 1 8 H K + Q L F M Q 1 4 H K + Q L F M Q 3 8 H K + Q L F M Q 1 2 H K + Q L F M Q 3 4 H K + Q L F M Q Values to Use in Formulas Threads per Inch F M Q

11 882 TAPS AN THRAING IS Table 10b. ANSI Standard Straight Pipe Taps (NPS) Cut Thread Limits ASM/ANSI B Threads per Inch, NPS, NPSC at Gaging Notch Pitch iameter Values to Use in Formulas Nominal Min. Max. A B C } } The following are approximate formulas, in which M = measured pitch diameter in inches: Major dia., min. = M + A Major dia., max. = M + B Minor dia., max. = M C All dimensions are given in inches. Lead Tolerance: Plus or minus inch per inch thread. Angle Tolerance: All pitches, plus or minus 45 min. in half angle and 68 min. in full angle. Taps made to these specifications are to be marked NPS and used for NPSC thread form. Table 10c. ANSI Standard Straight Pipe Taps (NPS) Ground Thread Limits ASM/ANSI B Nominal, Inches Threads per Inch, NPS, NPSC, NPSM Plug at Gaging Notch Major iameter Min. G Max. H Plug at Gaging Notch Pitch iameter Min. K Formulas for NPS Ground Thread Taps a Minor Threads Nominal Major iameter per Inch A B Min. G Max. H Max H (K + A) M B to 3 4 H (K + A) M B H (K + A) M B The maximum Pitch iameter tap is based upon an allowance deducted from the maximum product pitch diameter NPSC or NPSM, whichever is smaller. The minimum Pitch iameter tap is derived by subtracting the ground thread pitch diameter tolerance for actual equivalent size. a In the formulas, M equals the actual measured pitch diameter. All dimensions are given in inches. Lead tolerance: Plus or minus inch within any two threads not farther apart than one inch. Angle Tolerance: All pitches, plus or minus 30 min. in half angle. Taps made to these specifications are to be marked NPS and used for NPSC and NPSM. Max. L

12 TAPS AN THRAING IS 883 Table 11a. ANSI Standard Ground Thread Straight Fluted Taps Machine Screw s ASM/ANSI B Basic Major iam eter NC UNC Threads per Inch NF UNF Pitch Limits and Chamfers a No. NS UNS Flute s H1 H2 H3 H7 Overall A TPB PB TPB P TPB PB b PB TPB TPB TPB b PB P TPB TPB TPB b P PB TPB TPB b PB P TPB TPB b P PB PB TPB TPB TPB PB b P P TPB b P PB PB b PB PB PB TPB TPB TPB PB TPB * PB PB b P PB b P PB PB b PB PB PB TPB TPB TPB PB TPB TPB a Chamfer designations are: T = taper, P = plug, and B = bottoming. b Optional number flutes. All dimensions are given in inches. These taps are standard as high-speed steel taps with ground threads, with standard and optional number flutes and pitch diameter limits and chamfers as given in the table. These are style 1 taps and have external centers on thread and shank ends (may be removed on thread end bottoming taps). For standard thread limits see Table 6. For eccentricity tolerances see Table 25. Tolerances: Numbers 0 to 12 size range A, ± 1 32 ; B, ± 3 64 ; C, ± 1 32 ;, ;, Thread Square iameter Shank

13 884 TAPS AN THRAING IS Table 11b. ANSI Standard Cut Thread Straight Fluted Taps Machine Screw s ASM/ANSI B Threads per Inch HS Steel NS UNS NC UNC NF UNF Basic Carbon Steel Major iameter NC UNC NF UNF a Number Flutes Overall, A Thread, B imensions Square, C All dimensions are given in inches. Styles 1 and 2 cut thread taps have optional style centers on thread and shank ends. For standard thread limits see Table 7. For eccentricity tolerances see Table 25. Table 12. ANSI Standard Nut Taps ASM/ANSI B iameter Shank, Square, a 72 a a a 56 a a 36 a 40 a a a 36 a a 40 a a a a These taps are standard with plug chamfer only. All others are standard with taper, plug or bottoming chamfer. Tolerances for General imensions lement Range Tolerance lement Range Tolerance Overall, A 0 to 14 incl ± to 12 incl iameter Shank, 0 to 12 incl ± Thread, B 14 ± 1 16 Square, 0 to 14 incl Square, C 0 to 14 incl ± 1 32 Tap Threads per Inch NC,UNC Number Flutes Overall, A Thread, B Square, C iameter Shank, Square, Tolerances for General imensions lement iameter Range Tolerance lement iameter Range Tolerance Overall, A 1 4 to 1 2 ± 1 16 Shank iameter, 1 4 to Thread, B 1 4 to 1 2 ± 1 16 Square, 1 4 to Square, C 1 4 to 1 2 ± 1 32 All dimensions are given in inches. These ground thread high-speed steel taps are standard in H3 limit only. All taps have an internal center in thread end. For standard limits see Table 4. Chamfer J is made 1 2 ro 3 4 the thread length B.

14 TAPS AN THRAING IS 885 Table 13. ANSI Standard Spiral-Pointed Taps Machine Screw s ASM/ANSI B High-Speed Steel Taps with Ground Threads Basic Threads per No. Pitch Limits and iameter Major Inch Chamfers iameter NC UNC NF UNF NS UNS Flute s H1 H2 H3 H7 Overall A Thread B Square C Shank Square PB PB P P PB PB P PB P P P P PB P PB P PB P P PB PB PB PB P PB PB PB P P PB PB P PB PB PB P PB P High-Speed and Carbon Steel Taps with Cut Threads Threads per Inch Carbon Steel HS Steel Thread, B Square, C iameter Shank, Square, Basic Major iameter NC UNC NF UNF NC UNC NF UNF No. Flutes Overall, A Tolerances for General imensions Tolerance Tolerance Ground Cut Ground Cut lement Range Thread Thread lement Range Thread Thread Overall, A 0 to 12 ± 1 32 ± 1 32 Shank iameter, 0 to Thread, B 0 to 12 ± 3 64 ± 3 64 Square, C 0 to 12 ± 1 32 ± 1 32 Square, 0 to All dimensions are in inches. Chamfer designations are: P = plug and B = bottoming. Cut thread taps are standard with plug chamfer only. Style 1 ground thread taps have external centers on thread and shank ends (may be removed on thread end bottoming taps). Style 1 cut thread taps have optional style centers on thread and shank ends. Standard thread limits for ground threads are given in Table 6 and for cut threads in Table 7. For eccentricity tolerances see Table 25.

15 886 TAPS AN THRAING IS STYL 1 Table 14. ANSI Standard Spiral Pointed Only and Regular and Fast Spiral-Fluted Taps Machine Screw s ASM/ANSI B Pitch Limits Basic Major Threads per Inch No. & Chamfers a iameter iameter NC UNC NF UNF Flutes H2 H3 Overall, A Thread, B Square, C Shank, Square, 3 b PB PB PB PB c, 3 b PB c, 3 b PB d c, 3 b PB a Bottom chamfer applies only to regular and fast spiral-fluted machine screw taps. b Applies only to fast spiral-fluted machine screw taps. c oes not apply to fast spiral-fluted machine screw taps. d oes not apply to regular spiral-fluted machine screw taps. lement Overall, A Thread, B Square, C Tolerances for General imensions Range Tolerance lement 3 to 12 ± 1 Shank 32 iameter, 3 to 12 ± 3 64 Square, 3 to 12 ± 1 32 Range Tolerance 3 to to All dimensions are given in inches. These standard taps are made high-speed steel with ground threads. For standard thread limits see Table 6. For eccentricity tolerances see Table 25. Spiral Pointed Only Taps: These taps are standard with plug chamfer only. They are provided with a spiral point only; the balance the threaded section is left unfluted. These Style 1 taps have external centers on thread and shank ends. Regular Spiral Fluted Taps: These taps have right-hand spiral flutes with a helix angle from 25 to 35 degrees. Fast Spiral Fluted Taps: These taps have right-hand spiral flutes with a helix angle from 45 to 60 degrees. Both regular and fast spiral-fluted Style 1 taps have external centers on thread and shank ends (may be removed on thread end bottoming taps). Chamfer designations: P = plug and B = bottoming.

16 TAPS AN THRAING IS 887 Table 15a. ANSI Standard Ground Thread Straight Fluted Taps Fractional s ASM/ANSI B Threads per Inch No. Flute s Pitch iameter Limits and Chamfers imensions Tap NC UNC NF UNF H1 H2 H3 H4 H5 Overall, A Thread, B Square, C Shank, Square, TPB TPB TPB PB PB PB TBP PB PB PB TPB PB PB P TPB PB PB PB TPB PB PB PB TPB PB TPB PB P TPB PB PB TPB P TPB P P TPB P P TPB PB P TPB PB a 16 4 TPB P TPB PB P P TPB PB b TPB P TPB b 8 4 TPB TPB c 4 TPB TPB d 4 TPB d 4 TPB d 4 TPB a This size has 11 or 16 threads per inch NS-UNS. b These sizes are also available with plug chamfer in H6 pitch diameter limits. c This size has 14 threads per inch NS-UNS. d In these sizes NF-UNF thread taps have six flutes. Tolerances for General imensions lement iameter Range Tolerance lement iameter Range Tolerance 1 4 to 1 incl ± 1 32 iameter 4 to 5 8 incl Overall, A to incl ± 1 16 Shank, 16 to incl to 1 2 incl ± 1 16 Thread, B 9 16 to incl ± to 1 2 incl to 1 incl ± 1 Square, to 1 incl Square, C to incl ± to incl All dimensions are given in inches. These taps are standard in high-speed steel. Chamfer designations are: T = taper, P = plug, and B = bottoming. Style 2 taps, 3 8 inch and smaller, have external center on thread end (may be removed on bottoming taps) and external partial cone center on shank end with length come approximately one-quarter diameter shank. Style 3 taps, larger than 3 8 inch, have internal center in thread and shank ends. For standared thread limits see Table 4. For eccentricity tolerances see Table 25.

17 888 TAPS AN THRAING IS Table 15b. ANSI Standard Cut Thread Straight Fluted Taps Fractional s ASM/ANSI B Tap NC UNC Threads Per Inch Carbon Steel HS Steel NF UNF NS UNS NC UNC NF UNF No. Flutes Overall, A Thread, B imensions Square, C Shank, Square, , a b a 12 ba ba a a a Standard in plug chamfer only. b In these sizes NF-UNF thread taps have six flutes. Tolerances for General imensions lements Range Tolerance lements Range Tolerance 1 16 to 1 ± to 3 Overall, A to 2 ± 1 16 iameter Shank, 4 to to 3 16 ± to to 1 2 ± 1 16 Thread, B 9 16 to ± to to 2 ± 1 8 Square, 16 to to 1 ± to Square, C to 2 ± 1 16 All dimensions are given in inches. These taps are standard in carbon steel and high-speed steel. xcept where indicated, these taps are standard with taper, plug, or bottoming chamfer. Cut thread taps, sizes 3 8 inch and smaller have optional style center on thread and shank ends; sizes larger than 3 8 inch have internal centers in thread and shank ends. For standard thread limits see Table 3. For eccentricity tolerances see Table 25.

18 TAPS AN THRAING IS 889 Table 16. ANSI Standard Straight Fluted (Optional Number Flutes) and Spiral Pointed Taps Fractional s ASM/ANSI B Threads per- Inch No. Pitch iameter Limits and Chamfers ab Tap NC UNC NF UNF Flute s H1 H2 H3 H4 H5 Overall, A Thread, B Square, C Shank, Square, Ground Thread High-Speed-Steel Straight Fluted Taps PB P P PB P , 3 PB PB PB PB PB PB P P PB P Ground Thread High-Speed-Steel and Cut Thread High-Speed-Steel Spiral Pointed Taps P P PB P a P P P P PB P a P P P P PB P a P P P P PB P a P P P P P P P P P P P a Pc P P a 3 P P P P a P P d a P P e a Applies only to ground thread high-speed-steel taps. b Cut thread high-speed-steel taps are standard with plug chamfer only. c Applies only to tap. d Applies only to tap. e Applies ony to tap. For eccentricity tolerances see Table 25. lement Overall-, A Thread-, B Tolerances for General imensions iameter Tolerance iameter Tolerance Range Ground Thread Cut Thread lement Range Ground Thread CutThread Shankiameter, 1 4 to to 4 ± 32 ± to 1 2 ± 1 16 ± 1 16 Square, 1 4 to to 3 4 ± to Square, C 1 4 to 3 4 ± 1 32 All dimensions are given in inches. P = plug and B = bottoming. Ground thread taps Style 2, 3 8 inch and smaller, have external center on thread end (may be removed on bottoming taps) and external partial cone center on shank end, with length cone approximately 1 4 shank diameter. Ground thread taps Style 3, larger than 3 8 inch, have internal center in thread and shank ends. Cut threadtaps, 3 8 inch and smaller have optional style center on thread and shank ends; sizes larger than 3 8 inch have internal centers in thread and shank ends. For standard thread limits see Tables 3 and 4.

19 890 TAPS AN THRAING IS Table 17. Other Types ANSI Standard Taps ASM/ANSI B Tap NC UNC Threads per Inch NF UNF a Number Flutes 2 b, 3 a a 2 c, 3 a Overall, A Thread, B Square, C Shank, a oes not apply to spiral pointed only taps. b oes not apply to spiral fluted taps or to spiral fluted taps with 28 threads per inch. c Applies only to spiral pointed only taps. d Applies only to fast spiral fluted taps. Square, a d d lement Tolerances for General imensions iameter Range Tolerance lement Overall, A 1 4 to 1 2 ± 1 32 Thread, B 1 4 to 1 2 ± 1 16 Square, C 1 4 to 1 2 ± 1 32 Shank iameter, Square, iameter Range Tolerance 1 4 to to All dimensions are given in inches. These standard taps are made high-speed steel with ground threads. For standard thread limits see Table 4. Spiral Pointed Only Taps: These taps are standard with plulg chamfer only in H3 limit. They are provided with spiral point only. The balance the threaded section is left unfluted. Spiral Fluted Taps: These taps are standard with plug or bottoming chamfer in H3 limit and have right-hand spiral flutes with a helix angle from 25 to 35 degrees. Fast Spiral Fluted Taps: These taps are standard with plug or bottoming chamfer in H3 limit and have right-hand spiral flutes with a helix angle from 45 to 60 degrees. Style 2 taps, 3 8 inch and smaller, have external center on thread end (may be removed on bottoming taps) and external partial cone center on shank end with cone length approximately 1 4 shank diameter. Style 3 taps larger than 3 8 inch have internal center in thread and shank ends. For standard thread limits see Table 4. For eccentricity tolerances see Table 25.