MACHINE SCREWS AND NUTS Machinery's Handbook, 31st Edition
1775
MACHINE SCREWS AND NUTS American National Standard Machine Screws and Machine Screw Nuts This Standard ANSI/ASME B18.6.3 covers both slotted and recessed head machine screws. Dimensions of various types of slotted machine screws, machine screw nuts, and header points are given in Table 1 through Table 12 . The Standard also covers flat trim head, oval trim head and drilled fillister head machine screws and gives cross recess di - mensions and gaging dimensions for all types of machine screw heads. Information on metric machine screws B18.6.7M (Withdrawn) is given beginning on page 1790. Threads.— Except for sizes 0000, 000, and 00, machine screw threads may be either Uni fied Coarse (UNC) and Fine thread (UNF) Class 2A (see American Standard for Unified Screw Threads starting on page 1947 ) or UNRC and UNRF Series, at option of manufac turer. Thread dimensions for sizes 0000, 000, and 00 are given in Table 7 on page 1780. Threads for hexagon machine screw nuts may be either UNC or UNF, Class 2B, and for square machine screw nuts are UNC Class 2B. Length of Thread.— Machine screws of sizes No. 5 and smaller with nominal lengths equal to 3 diameters and shorter have full form threads extending to within 1 pitch (thread) of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than 3 diameters, up to and including 1 1 ∕ 8 inch, have full form threads extending to within two pitches (threads) of the bearing surface of the head, or closer, if practicable. Unless other wise specified, screws of longer nominal length have a minimum length of full form thread of 1.00 inch. Machine screws of sizes No. 6 and larger with nominal length equal to 3 diam eters and shorter have full form threads extending to within 1 pitch (thread) of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than 3 diameters, up to and including 2 inches, have full form threads extending to within 2 pitches (threads) of the bearing surface of the head, or closer, if practicable. Screws of longer nominal length, unless otherwise specified, have a minimum length of full form thread of 1.50 inches. Table 1. Square and Hexagon Machine Screw Nuts ANSI/ASME B18.6.3-1972 (R1991) F H H
F
Optional; See Note
G 1
G
30
30
Nom. Size
Basic Dia. 0.0600 0.0730 0.0860 0.0990 0.1120 0.1250 0.1380 0.1640 0.1900 0.2160 0.2500 0.3125 0.3750
Basic F
Max. F 0.156 0.156 0.188 0.188 0.250 0.312 0.312 0.344 0.375 0.438 0.438 0.562 0.625
Min. F 0.150 0.150 0.180 0.180 0.241 0.302 0.302 0.332 0.362 0.423 0.423 0.545 0.607
Max. G
Min. G
Max. G 1
Min. G 1
Max. H
Min. H
0 1 2 3 4 5 6 8
0.221 0.206 0.180 0.171 0.050 0.043 0.221 0.206 0.180 0.171 0.050 0.043 0.265 0.247 0.217 0.205 0.066 0.057 0.265 0.247 0.217 0.205 0.066 0.057 0.354 0.331 0.289 0.275 0.098 0.087 0.442 0.415 0.361 0.344 0.114 0.102 0.442 0.415 0.361 0.344 0.114 0.102 0.486 0.456 0.397 0.378 0.130 0.117 0.530 0.497 0.433 0.413 0.130 0.117 0.619 0.581 0.505 0.482 0.161 0.148 0.619 0.581 0.505 0.482 0.193 0.178 0.795 0.748 0.650 0.621 0.225 0.208
5 ∕ 32 5 ∕ 32 3 ∕ 16 3 ∕ 16 5 ∕ 16 5 ∕ 16 1 ∕ 4
11 ∕ 32
10 12 1 ∕ 4
3 ∕ 8
7 ∕ 16 7 ∕ 16 9 ∕ 16
5 ∕ 16
3 ∕ 8 0.884 0.833 0.722 0.692 0.257 0.239 All dimensions in inches. Hexagon machine screw nuts have tops flat and chamfered. Diameter of top circle should be the maximum width across flats within a tolerance of minus 15 percent. Bottoms are flat but may be chamfered if so specified. Square machine screw nuts have tops and bottoms flat without chamfer. 5 ∕ 8
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