HEX KEY SIZES CHART


Hex key socket sizes chart according to ASME B18.3 standard.


Dimensions of Hex Keys and Bits
Dimensions of Hexagon Keys and Bits
Nom.
Key / Bit
&
Socket
Size 
W Y B C R L K
Max. Min. Max. Min. Max. Min. Short
Series
Long
Series
Max. Min. Max. Min.
- 0.028 0.0280 0.0275 0.0314 0.0300 0.312 0.125 1.312 1.125 2.688 2.500 0.062 - 0.003
- 0.035 0.0350 0.0345 0.0393 0.0378 0.438 0.250 1.312 1.125 2.766 2.578 0.062 - 0.004
- 0.050 0.0500 0.0490 0.0560 0.0540 0.625 0.438 1.750 1.562 2.938 2.750 0.062 - 0.006
1/16 0.062 0.0625 0.0615 0.0701 0.0680 0.656 0.469 1.844 1.656 3.094 2.906 0.062 - 0.008
5/64 0.078 0.0781 0.0771 0.0880 0.0859 0.703 0.516 1.969 1.781 3.281 3.094 0.078 - 0.008
3/32 0.094 0.0937 0.0927 0.1058 0.1035 0.750 0.562 2.094 1.906 3.469 3.281 0.094 - 0.009
7/64 0.109 0.1094 0.1079 0.1238 0.1210 0.797 0.609 2.219 2.031 3.656 3.469 0.109 - 0.014
1/8 0.125 0.1250 0.1235 0.1418 0.1390 0.844 0.656 2.344 2.156 3.844 3.656 0.125 - 0.015
9/64 0.141 0.1406 0.1391 0.1593 0.1566 0.891 0.703 2.469 2.281 4.031 3.844 0.141 - 0.016
5/32 0.156 0.1562 0.1547 0.1774 0.1745 0.938 0.750 2.594 2.406 4.219 4.031 0.156 - 0.016
3/16 0.188 0.1875 0.1860 0.2135 0.2105 1.031 0.844 2.844 2.656 4.594 4.406 0.188 - 0.022
Nom.
Key / Bit
&
Socket
Size 
W Y B C R L K
Max. Min. Max. Min. Max. Min. Short
Series
Long
Series
Max. Min. Max. Min.
7/32 0.219 0.2187 0.2172 0.2490 0.2460 1.125 0.938 3.094 2.906 4.969 4.781 0.219 - 0.024
1/4 0.250 0.2500 0.2485 0.2845 0.2815 1.219 1.031 3.344 3.156 5.344 5.156 0.250 - 0.030
5/16 0.312 0.3125 0.3110 0.3570 0.3531 1.344 1.156 3.844 3.656 6.094 5.906 0.312 - 0.032
3/8 0.375 0.3750 0.3735 0.4285 0.4238 1.469 1.281 4.344 4.156 6.844 6.656 0.375 - 0.044
7/16 0.438 0.4375 0.4355 0.5005 0.4944 1.594 1.406 4.844 4.656 7.594 7.406 0.438 - 0.047
1/2 0.500 0.5000 0.4975 0.5715 0.5650 1.719 1.531 5.344 5.156 8.344 8.156 0.500 - 0.050
9/16 0.562 0.5625 0.5600 0.6420 0.6356 1.844 1.656 5.844 5.656 9.094 8.906 0.562 - 0.053
5/8 0.625 0.6250 0.6225 0.7146 0.7080 1.969 1.781 6.344 6.156 9.844 9.656 0.625 - 0.055
3/4 0.750 0.7500 0.7470 0.8580 0.8512 2.219 2.031 7.344 7.156 11.344 11.156 0.750 - 0.070
Nom.
Key / Bit
&
Socket
Size 
W Y B C R L K
Max. Min. Max. Min. Max. Min. Short
Series
Long
Series
Max. Min. Max. Min.
7/8 0.875 0.8750 0.8720 1.0020 0.9931 2.469 2.281 8.344 8.156 12.844 12.656 0.875 - 0.076
1 1.000 1.0000 0.9970 1.1470 1.1350 2.719 2.531 9.344 9.156 14.344 14.156 1.000 - 0.081
1 1/4 1.250 1.2500 1.2430 1.4337 1.4138 3.250 2.750 11.500 11.000 - - 1.250 3.750 0.092
1 1/2 1.500 1.5000 1.4930 1.7204 1.6981 3.750 3.250 13.500 13.000 - - 1.500 4.500 0.104
1 3/4 1.750 1.7500 1.7430 2.0072 1.9825 4.250 3.750 15.500 15.000 - - 1.750 5.250 0.115
2 2.000 2.0000 1.9930 2.2939 2.2668 4.750 4.250 17.500 17.000 - - 2.000 6.000 0.126
2 1/4 2.250 2.2500 2.2430 2.5807 2.5511 5.250 4.750 19.500 19.000 - - 2.250 6.750 0.137
2 3/4 2.750 2.7500 2.7420 3.1541 3.1187 6.250 5.750 23.500 23.000 - - 2.750 8.250 0.159
3 3.000 3.0000 2.9920 3.4409 3.4030 6.750 6.250 25.500 25.000 - - 3.000 9.000 0.171
Nom.
Key / Bit
&
Socket
Size 
Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. R L K
W Y B Short
Series
Long
Series
C

Symbols: W = Hexagon Width Across Flats, Y = Hexagon Width Across Corners, R = Minimum Radius of Bend, L = Length of Bit, K = Maximum Champfer

Notes:

  • Hexagon Keys are furnished as Short Arm Series or Long Arm Series.
  • Designation Examples:
    • Hexagon Key, ASME B18.3, 1⁄8 Short Arm Series
    • Hexagon Key Bit, ASME B18.3, 11⁄2 Hex

Reference:

  • ASME B18.3-2003, Socket Cap, Shoulder, Set Screws, Hex, and Spline Keys