Inch series · technical reference

Socket Head Cap Screw Dimensions

Reference dimensions for inch-series hexagon socket head cap screws. The drawing uses an original CAD projection of a 1/4-20 UNC × 1 in reference instance; choose the exact UNC or UNF thread and L from the product listing.

Source: ASME B18.3 record in U.S. DoD ASSIST.

StandardASME B18.3 · Inch Series
RevisionSource review · 2026-08
Unitsinches
CAD ORTHOGRAPHIC REFERENCEASME B18.3.1A · INCH SERIES REFERENCE
ASME B18.3.1A socket head cap screw dimension drawing, side view with dimension callouts, 1/4-20 UNC reference size
SIDE VIEW · LENGTH UNDER HEAD · 1/4-20 UNC
ASME B18.3.1A socket head cap screw dimension drawing, end view showing hex socket and head diameter, 1/4-20 UNC reference size
END VIEW · HEX SOCKET · 1/4-20 UNC

Reference size shown: 1/4-20 UNC. The drawing identifies dimension locations only. Use the table for nominal data and confirm the exact product configuration before ordering.

Reference head dimensions · inch series
Nominal threadUNC / UNF (TPI)Head diameter (A) max / minHead height (H) max / minHex key (J)Key engagement min (T)
#0— / 800.096 / 0.0910.060 / 0.0570.0500.025
#256 / 640.140 / 0.1340.086 / 0.0835/640.038
#348 / 560.161 / 0.1540.099 / 0.0955/640.044
#440 / 480.183 / 0.1760.112 / 0.1083/320.051
#632 / 400.226 / 0.2180.138 / 0.1347/640.064
#832 / 360.270 / 0.2620.164 / 0.1599/640.077
#1024 / 320.312 / 0.3030.190 / 0.1855/320.090
1/4 in20 / 280.375 / 0.3650.250 / 0.2443/160.120
5/16 in18 / 240.469 / 0.4570.312 / 0.3061/40.151
3/8 in16 / 240.562 / 0.5500.375 / 0.3685/160.182
7/16 in14 / 200.656 / 0.6420.438 / 0.4303/80.213
1/2 in13 / 200.750 / 0.7350.500 / 0.4923/80.245
5/8 in11 / 180.938 / 0.9210.625 / 0.6161/20.307
3/4 in10 / 161.125 / 1.1070.750 / 0.7405/80.370
7/8 in9 / 141.312 / 1.2930.875 / 0.8643/40.432
1 in8 / 121.500 / 1.4791.000 / 0.9883/40.495
1-1/8 in7 / 121.688 / 1.6651.125 / 1.1117/80.557
1-1/4 in7 / 121.875 / 1.8521.250 / 1.2367/80.620
1-3/8 in6 / 122.062 / 2.0381.375 / 1.36010.682
1-1/2 in6 / 122.250 / 2.2241.500 / 1.48510.745

From the catalog

Related products in the catalog

Browse Socket Screws and confirm the head style, drive, thread and size against this reference.

View all
Titanium Socket Head Cap Screws DIN 912 Grade 3 Grade 4 UNC UNF Plain Natural Finish Automotive Racing Motorcycle Fasteners Titanium Socket Head Cap Screws DIN 912 Grade 3 Grade 4 UNC UNF Plain Natural Finish Automotive Racing Motorcycle Fasteners View Product Internal Hex Titanium Socket Head Cap Screws UNC UNF ASME B18.3 Plain Natural Finish Aerospace Marine Chemical Medical Oil Gas Internal Hex Titanium Socket Head Cap Screws UNC UNF ASME B18.3 Plain Natural Finish Aerospace Marine Chemical Medical Oil Gas View Product Titanium Socket Head Cap Screws Grade 3 Grade 4 DIN 912 GB70.1 UNC UNF Plain Natural Finish for Aerospace Marine Fasteners Titanium Socket Head Cap Screws Grade 3 Grade 4 DIN 912 GB70.1 UNC UNF Plain Natural Finish for Aerospace Marine Fasteners View Product Titanium Hex Drive Socket Cap Screws Grade 3 4 UNC UNF ASME B18.3 Plain Natural Finish Automotive Racing Industrial Fasteners Titanium Hex Drive Socket Cap Screws Grade 3 4 UNC UNF ASME B18.3 Plain Natural Finish Automotive Racing Industrial Fasteners View Product