JIS B 1181 Hexagon Nuts

Unified hexagon head bolts and screws - Normal series

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Nominal size
D		 Number of threads per inch Diameter of threaded portion of shank
B		 Width across flats
A		 Width across corners
C		 Diameter of washer face
E		 Thickness of head
F		 Radius under head
R		 Split cotter pin holes.See clause 15
Diameter of hole Drill sizes Maximum off-centre distance between centre line of hole and thread
UNC UNF Max. Min. Max. Min. Max. Max. Min. Max. Min. Max. Min. Max. Min.
in in in in in in in in in in in in in in mm in
1/4 20 28 0.2500 0.2465 0.4375 0.4305 0.505 0.421 0.411 0.163 0.153 0.025 0.015 0.084 0.079 2.00 0.006
5/16 18 24 0.3125 0.3090 0.5000 0.4930 0.577 0.483 0.473 0.211 0.201 0.025 0.015 0.100 0.095 2.40 0.006
3/8 16 24 0.3750 0.3715 0.5625 0.5545 0.650 0.545 0.535 0.243 0.233 0.025 0.015 0.117 0.112 2.85 0.006
7/16 14 20 0.4375 0.4335 0.6250 0.6170 0.722 0.605 0.595 0.291 0.281 0.025 0.015 0.117 0.112 2.85 0.007
1/2 13 20 0.5000 0.4960 0.7500 0.7420 0.866 0.730 0.720 0.323 0.313 0.025 0.015 0.152 0.146 3.70 0.007
a 9/16 12 18 0.5625 0.5585 0.8125 0.8045 0.938 0.792 0.782 0.371 0.361 0.045 0.020 0.152 0.146 3.70 0.008
5/8 11 18 0.6250 0.6190 0.9375 0.9295 1.083 0.918 0.908 0.403 0.393 0.045 0.020 0.184 0.177 4.50 0.008
3/4 10 16 0.7500 0.7440 1.1250 1.1150 1.300 1.100 1.090 0.483 0.463 0.045 0.020 0.184 0.177 4.50 0.009
7/8 9 14 0.8750 0.8670 1.3125 1.3005 1.515 1.285 1.275 0.563 0.543 0.065 0.040 0.184 0.177 4.50 0.009
1 8 12 1.0000 0.9920 1.5000 1.4880 1.732 1.473 1.463 0.627 0.597 0.095 0.060 0.222 0.213 5.40 0.010
1 1/8 7 1.1250 1.1170 1.6875 1.6575 1.948 1.641 1.625 0.718 0.678 0.095 0.060 0.222 0.213 5.40 0.010
1 1/4 7 1.2500 1.2420 1.8750 1.8300 2.165 1.813 1.797 0.813 0.773 0.095 0.060 0.254 0.244 6.20 0.011
a 1 3/8 6 1.3750 1.3650 2.0625 2.0175 2.382 2.001 1.985 0.878 0.838 0.095 0.060 0.254 0.244 6.20 0.011
1 1/2 6 1.5000 1.4900 2.2500 2.2050 2.598 2.188 2.172 0.974 0.934 0.095 0.060 0.290 0.280 7.10 0.011
1 3/4 5 1.7500 1.7400 2.6250 2.5650 3.031 2.543 2.527 1.134 1.074 0.095 0.060 0.353 0.343 8.70 0.012
2 4½ 2.0000 1.9900 3.0000 2.9400 3.464 2.918 2.902 1.263 1.203 0.095 0.060 0.353 0.343 8.70 0.015

NOTE: In the case of the 7/16 in and 9/16 in bolt heads, the width across flats is 1/16 in smaller than that of the corresponding nuts. This is in accordance with the American Standard from which these sizes are derived.

a To be dispensed with wherever possible.

b When bolts from 1/4 in to 1 in nominal size are hot forged, the tolerance on the width across flats shall be two and a half times the tolerance shown in the table.