Dimensions of Finished Hexagonal Headed Bolts (ASA B18.2-1952)

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This table contains dimensions of finished hexagonal headed bolts ranging in thread size from 1/4 inch to 3 inch nominal diameter.

This table includes maximum and minimum screw head width and height, (across flats and conrners) as well as maximum screw shaft diameter information.

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(Vallory H. Laughner and Augustus D. Hargan, "Handbook of Fastening and Joining of Metal Parts," McGraw-Hill Company, New York, 1956.)

NOTES: All dimensions are in inches. "Finished" in the title refers to the quality of manufacture and the closeness of tolerance and does not indicate that surfaces are completely machined. Taper of head (angle between one side and axis) shall not exceed 2 degrees, specified width across flats being the largest dimension. Top of head shall be flat and chamfered. Diameter of top circle shall be maximum width across flats within a tolerance of minus 15 percent. Bearing surface shall be flat and either washer-faced or with chamfered corners. Diameter of bearing surface shall be 95 percent of maximum width across flats within a tolerance of plus or minus 5 percent. Bearing surface shall be at right angles to axis of body within a tolerance of 2 degrees for sizes up to and including 1 in, and within a tolerance of 1 degree for sizes larger than 1 in. The bearing surface shall be concentric with axis of body within a tolerance of 3 percent of the maximum width across the flats. Minimum thread length shall be twice the diameter plus 1/4 in for lengths up to and including 6 in; twice the diameter plus 1/2 in for lengths over 6 in. The tolerance shall be plus 3/16 in or 2-1/2 threads, whichever is greater. On products that are too short for minimum thread lengths, the distance from the bearing surface of the head to the first complete thread shall not exceed the length of 2-1/2 threads, as measured with a ring thread gauge, for sizes up to and including 1 in and 3-1/2 threads for sizes larger than 1 in. Threads shall be coarse, fine, or 8-thread series, class 2A for plain (unplated) bolts. For plated bolts, the diameters may be increased by the amount of class 2A allowance. Thickness or quality of plating shall be measured or tested on the side of the head. Point shall be flat and chamfered, length of point to first full thread not to exceed 1-1/2 threads. Tolerance on length for sizes up to and including 3/4 in shall be minus 1/32 in for lengths up to and including 1 in; minus 1/16 in for lengths over 1 in to and including 2 in; and minus 3/32 in for lengths over 2 in to 6 in, inclusive. The tolerance shall be doubled for sizes over 3/4 in and lengths longer than 6 in. Total runout (eccentricity and angularity) of thread in relation to body for sizes up to and including 3/4 in shall not exceed 0.010 in for each inch of length when measured in a sleeve gauge; the deviation of shank from a surface plate on which it is rolled shall not exceed 0.0312 in. A suggested gauge is shown in the Appendix. For sizes over 3/4 in total runout shall be subject to negotiation. Unless otherwise specified, physical properties of steel bolts shall correspond to SAE Grades 2 or 5. Bolts may also be made from alloy steel, brass, bronze, corrosion-resisting steel, aluminum alloy, or such other material as specified.

 
Nominal Body diameter Width across Radius
size or minimum Width across flats corners Height of fillet
basic major (maximum F G H R
diameter equal to --------------------- ------------ ------------------- -----------
of thread nominal size) Max (basic) Min* Max Min Nom Max Min Max Min
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# 1/4 0.2500 0.2450 7/16 0.4375 0.428 0.505 0.488 5/32 0.163 0.150 0.023 0.009
# 5/16 0.3125 0.3065 1/2 0.5000 0.489 0.5777 0.557 13/64 0.211 0.195 0.023 0.009
# 3/8 0.3750 0.3690 9/16 0.5625 0.551 0.650 0.628 15/64 0.243 0.226 0.023 0.009
# 7/16 0.4375 0.4305 5/8 0.6250 0.612 0.722 0.698 9/32 0.291 0.272 0.023 0.009 
# 1/2 0.5000 0.4930 3/4 0.7500 0.736 0.866 0.840 5/16 0.323 0.302 0.023 0.009
# 9/16 0.5625 0.5545 13/16 0.8125 0.798 0.938 0.910 23/64 0.371 0.348 0.041 0.021
# 5/8 0.6250 0.6170 15/16 0.9375 0.922 1.083 1.051 25/64 0.403 0.378 0.041 0.021
# 3/4 0.7500 0.7410 1-1/8 1.1250 1.100 1.299 1.254 15/32 0.483 0.455 0.041 0.021
# 7/8 0.8750 0.8660 1-5/16 1.3125 1.285 1.516 1.465 35/64 0.563 0.531 0.062 0.047
# 1 1.0000 0.9900 1-1/2 1.5000 1.469 1.732 1.675 39/64 0.627 0.591 0.062 0.047
 1-1/8 1.1250 1.1140 1-11/16 1.6875 1.631 1.949 1.859 11/16 0.718 0.658 0.125 0.110
 1-1/4 1.2500 1.2390  1-7/8 1.8750 1.812 2.165 2.066 25/32 0.813 0.749 0.125 0.110
 1-3/8 1.3750 1.3630 2-1/16 2.0625 1.994 2.382 2.273 27/32 0.878 0.810 0.125 0.110
 1-1/2 1.5000 1.4880 2-1/4 2.2500 2.175 2.598 2.480 15/16 0.974 0.902 0.125 0.110
 1-5/8 1.6250 1.6130 2-7/16 2.4375 2.356 2.815 2.686 1 0.974 0.902 0.125 0.110
 1-3/4 1.7500 1.7380 2-5/8 2.6250 2.538 3.031 2.893 1-3/32 0.974 0.902 0.125 0.110
 1-7/8 1.8750 1.8630 2-13/16 2.8125 2.719 3.248 3.100 1-5/32 0.974 0.902 0.125 0.110
 2 2.0000 1.9880 3 3.0000 2.900 3.464 3.306 1-7/32 0.974 0.902 0.125 0.110
 2-1/4 2.2500 2.2380 3-3/8 3.3750 3.262 3.897 3.719 1-3/8 0.974 0.902 0.188 0.173
 2-1/2 2.5000 2.4880 3-3/4 3.7500 3.625 4.330 4.133 1-17/32 0.974 0.902 0.188 0.173
 2-3/4 2.7500 2.7380 4-1/8 4.1250 3.988 4.763 4.546 1-11/16 0.974 0.902 0.188 0.173
 3 3.0000 2.9880 4-1/2 4.5000 4.350 5.196 4.959 1-7/8 0.974 0.902 0.188 0.173
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* In sizes 1/4 to 1 inch a tolerance of minus 0.050 D may be used when the product is hot made.
# Products unified dimensionally with British and Canadian standards.