Machinery's Handbook, 31st Edition
1704 Fasteners for Structural Applications (1) Top of Head : Top of head shall be full form and chamfered or rounded with the diameter of chamfer circle or start of rounding being equal to the maximum width across flats within a tolerance of − 15%. (2) Head Taper : Maximum width across flats shall not be exceeded. No transverse section through the head between 25 and 75 percent of actual head height, as measured from the bear- ing surface, shall be less than the minimum width across flats. (3) Bearing Surface : Bearing surface shall be flat and washer faced. Diameter of washer face shall be equal to the maximum width across flats within a tolerance of − 10%. Thickness of the washer face shall be not less than 0.015 inch nor greater than 0.025 inch for bolt sizes 3 ∕ 4 inch and smaller; and not less than 0.015 inch nor greater than 0.035 inch for sizes larger than 3 ∕ 4 inch. The plane of the bearing surface shall be perpendicular to the axis of the body within the FIM limits specified for total runout. Measurement of FIM shall extend as close to the periph - ery of the bearing surface as possible while the bolt is being held in a collet or other gripping device at a distance of one bolt diameter from the underside of the head. (4) True Position of Head : The axis of the head shall be located at true position with re - spect to the axis of the body (determined over a distance under the head equal to one diam - eter) within a tolerance zone having a diameter equivalent to 6 percent of the maximum width across flats at maximum material condition. (5) Body Diameter : Any swell or fin under the head or any die seam on the body should not ex - ceed the basic bolt diameter by the following: 0.030 in, for sizes 1 ∕ 2 inch; 0.050 inch for sizes 5 ∕ 8 and 3 ∕ 4 inch; 0.060 inch for sizes over 3 ∕ 4 inch to 1 1 ∕ 4 inch; 0.090 inch for sizes over 1 1 ∕ 4 inch. (6) Point : Point shall be chamfered or rounded at the manufacturer’s option from approxi - mately 0.016 inch below the minor diameter of the thread. The first full formed thread at major diameter is located a distance no greater than 2 times the pitch measured from the end of the screw. This distance is to be determined by measuring how far the point enters into a cylindri- cal NOT GO major diameter ring gage. (7) Straightness : Shanks of bolts shall be straight within the following limits at MMC; for bolts with nominal lengths to and including 12 inches the maximum camber shall be 0.006 inch per inch (0.006L) of bolt length, and for bolts with nominal lengths over 12 inches to and including 24 inches the maximum camber shall be 0.008 inch per inch (0.008L) of length. (8) Bolt Length : Bolts are normally supplied in 1 ∕ 4 inch length increments, all lengths. (9) Length Tolerance : Bolt length tolerances shall be as tabulated below:
Nominal Bolt Size Nominal Bolt Length Through 6 inches
3 ∕ 4 through 1 1 1 ∕
8 through 1
1 ∕
1 ∕
5 ∕
2
8
2
Tolerance of Length
− 0.12 − 0.19
− 0.12 − 0.25
− 0.19 − 0.25
− 0.25
Over 6 inches − 0.25 (10) Thread Length : The length of thread on bolts shall be controlled by the grip gaging length, LG, max., and the body length, L B , min., as follows. Grip gaging length, L G , max., is the distance measured parallel to the axis of bolt from the underhead bearing surface to the face of a noncounterbored or noncountersunk standard G0 thread ring gage assembled by hand as far as the thread will permit. It shall be used as the criterion for inspection. The maximum grip gaging length, as calculated and rounded to two decimal places for any bolt not threaded full length, shall be equal to the nominal bolt length minus the basic thread length ( L G , max. = L nom − L T ). For bolts which are threaded full length, L G , max. defines the unthreaded length under the head and shall not exceed the length of 2.5 times the thread pitch for sizes up to and including 1 inch, and 3.5 times the thread pitch for sizes larger than 1 inch, L G , max. represents the minimum design grip length of the bolt and may be used for determining thread availability when selecting bolt lengths even though us - able threads may extend beyond this point. Basic thread length, L T , is a reference dimension, intended for calculation purposes only, which represents the distance from the extreme end of the bolt to the last complete (full form) thread.
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