Nuts
H
G
F
H
Machine Screw Nuts
Hex &
Square
S
QUARE AND
H
EX
M
ACHINE
S
CREW
N
UTS
ANSI/ASME B18.6.3
Nominal Size or Basic
Thread Diameter
F G G1 H
Width Across Flats
Width Across Corners
Thickness
Square Hex
Basic Max Min Max Min Max Min Max Min
0 0.0600 5/32 0.156 0.150 0.221 0.206 0.180 0.171 0.050 0.043
1 0.0730 5/32 0.156 0.150 0.221 0.206 0.180 0.171 0.050 0.043
2 0.0860 3/16 0.188 0.180 0.265 0.247 0.217 0.205 0.066 0.057
3 0.0990 3/16 0.188 0.180 0.265 0.247 0.217 0.205 0.066 0.057
4 0.1120 1/4 0.250 0.241 0.354 0.331 0.289 0.275 0.098 0.087
5 0.1250 5/16 0.312 0.302 0.442 0.415 0.361 0.344 0.114 0.102
6 0.1380 5/16 0.312 0.302 0.442 0.415 0.361 0.344 0.114 0.102
8 0.1640 11/32 0.344 0.332 0.486 0.456 0.397 0.378 0.130 0.117
10 0.1900 3/8 0.375 0.362 0.530 0.497 0.433 0.413 0.130 0.117
12 0.2160 7/16 0.438 0.423 0.619 0.581 0.505 0.482 0.161 0.148
1/4 0.2500 7/16 0.438 0.423 0.619 0.581 0.505 0.482 0.193 0.178
5/16 0.3125 9/16 0.562 0.545 0.795 0.748 0.650 0.621 0.225 0.208
3/8 0.3750 5/8 0.625 0.607 0.884 0.833 0.722 0.692 0.257 0.239
Description
Hex Machine Screw Nut: A six-sided internally threaded fastener with flat tops and chamfered corners. Threads shall be
Unified Standard, Class 2B.
Square Machine Screw Nut: A four-sided, internally threaded fastener, tops and bottoms flat, without chamfer. Threads shall
be Unified coarse thread, Class 2B.
Applications/
Advantages
Hex Machine Screw Nut: Designed to be used specifically with machine screws. Stainless nuts are used with stainless
machine screws where parts are subject to corrosive conditions.
Square Machine Screw Nut: Offers a greater bearing surface for wrenching.
Material
Steel: Any low carbon steel
Stainless: 18-8 stainless steel
Plating
See Appendix-A for plating information.
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