Fastener Math and Terminology

Transcription

1 Fastener Math and Terminology There are some things about dealing with fasteners that will be easier if you understand the terms and mathematics associated with them. To many of you this will be a review, to some of you it will be new. It is my hope that it will help all of you, at least with your fastener aspects. Terminology Grip Length: The grip length of a fastener is always the unthreaded (solid) part of the shank. The grip length does not include the head on a protruding head fastener, however the grip length does include the head on a countersunk head fastener. The Grip of a fastener starts at the head (included or excluded as applicable) and continues to the full cylindrical portion of the shank. The Grip Length does not include the Transition Area or the Threaded part of the fastener. In the case where the fastener has no threads but has a cross-drilled hole for retention, such as a clevis pin, then the grip ends at the beginning of the hole. Some fasteners such as Hi-Shear Rivets or Lockbolts with collars have neither hole nor threads. In this case the grip ends at the end of the full cylindrical portion of the shank or a little earlier if the manufacturer allows room for collar installation. Fasteners that are fully threaded do not have a grip length. Shank: The unthreaded part of a fastener. The shank is always a part of, if not all of the Grip Length of the fastener. The shank does not include the head of the fastener. Transition Area: The part of the fastener where the Shank starts to reduce in dimension to allow the threads to be formed. The Transition Area includes the imperfect threads and extends just until the threads are fully formed. Inf1

2 Threads: This is the part of the fastener that is best described as a helical formed triangular strip. On a male fastener such as a bolt or screw it usually starts at the end of the grip or just under the Head of the fastener. The threads are formed by a process called rolling or by an older process called cutting. The threads are the part of the male fastener that the nut screws or threads onto by rotating its matching internal threads until both the nut and the fastener have fully engaged. Thread Area: This includes the Transition area (between the Shank and the Threads) and the Threads. This is measured from the end of the full cylindrical portion of the shank (where the Grip ends), to the end of the fastener. Overall Length: The overall length is the sum of the Grip Length, The Transition Area and the Thread Length. The Overall length of a fastener starts at the head (included or excluded as applicable) and continues to the end of the fastener. The Overall Length does include the Grip, the Transition Area, and the Threaded part of the fastener. In the case where the fastener has no threads but has a cross-drilled hole for retention, such as a clevis pin, then the Overall Length ends at the end of the fastener regardless of the hole. Decimal/Fractional Charts have been made in many styles and forms. Sometimes the Chart helps to put things into perspective. Remember, people think about values in many different ways. Inf2

3 Fastener Math For some of you this will be a review, for some it will be a numerical revelation. So in either case be patient, with yourself or with me whichever the case may be. It may help some people to refer to the Summary on page 7 for the formulas without the instructions. Some of us were raised in times when math was stressed more in school and some of us only learned how to add and subtract. For this reason we will do all of our exercises using a calculator or Decimal/fractional chart. The first thing is to realize that there are so many different ways a number or a fraction may be written or looked at that it surprises most people. For example: One quarter could be looked at in so many ways, and some people are accustomed to relating to it in only one way. See below: Inf3

4 Fractional Terms The number in a fraction that is to the left of the division sign, or /, or on the top of the division line as in 1 is called the numerator. 16 The number on the bottom or the right is called the denominator. Examples of one 16 th are: 1, 1/16 or Converting Numbers with Decimals into Fractions 1) Select the desired denominator you are looking for such as 16 ths of an inch, which is a useful denominator because most of the MS and NAS bolts grip lengths are measured in 16 ths. 2) Using the calculator multiply your decimal figure by your fractional denominator. For an example we will use.8125 for our decimal figure. On the calculator input.8125, then the x key, then input 16, then the = key. The answer you should have come up with is 13 on the display of the calculator. Or as we will complete the mathematical statement on paper, 13/16 ths of an inch. Inf4

5 Converting Fractions into Decimals 1) Using the calculator enter the numerator, then the key, then enter the denominator, then the = key. This will give you a decimal number. 2) As an example we will convert the fraction 13 or 13/16 or ) Using the calculator enter 13, then, then 16, then = The answer you should have come up with is.8125, that is the decimal equivalent for 13/16 ths. Decimal/Fractional Charts For the ease of use and to cover situations where a calculator is not handy, Decimal/Fractional Charts have been made in many styles and forms. Sometimes the Chart helps to put things into perspective. Remember, people think about values in many different ways. Please see the Decimal/Fraction Chart on the following page. Notice that it goes all the way to 1/64 ths. Inf5

6 Inf6 Genuine Aircraft Hardware Co.

7 Summary The Overall Length of a fastener is: Grip Length + Transition Area + Thread Length Overall Length To convert decimals into fractions, multiply the decimal by the desired fractional denominator. This will become the numerator. Decimal x Fractional Denominator = Numerator. Or... Multiples of the Denominator = Numerator To convert fractions into decimals, divide the numerator by the denominator. Numerator = Decimal Number Denominator Additional Information: Whenever, in a fraction, the numerator is larger than the denominator, then the value is greater than one. This is called an Improper Fraction. You will need to simplify it by separating the Whole numbers out and simplifying or converting the remaining proper fraction. I.e. 24/16 = 1.5 or 24/16 = ((16/16) + (8/16)) Compare 1.5 = Inf7

8 Notes Inf8