Inch series · technical reference

Button Head Socket Cap Screw Dimensions

Reference dimensions for hexagon socket button head cap screws. This chart covers the ASME B18.3 inch-series form, not a generic pan-head or low-profile substitute.

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

StandardASME B18.3.3A · Inch Series
RevisionSource review · 2026-08
Unitsinches
CAD ORTHOGRAPHIC REFERENCEASME B18.3.3A · INCH SERIES REFERENCE
ASME B18.3.3A button head socket cap screw dimension drawing, side view with dimension callouts, 1/4-20 UNC reference size
SIDE VIEW · LENGTH REFERENCE · 1/4-20 UNC
ASME B18.3.3A button head socket cap screw dimension drawing, end view showing hex socket and button head diameter, 1/4-20 UNC reference size
END VIEW · HEAD / DRIVE · 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)
#256 / 640.164 / 0.1540.046 / 0.0380.0500.028
#348 / 560.188 / 0.1760.052 / 0.0441/160.035
#440 / 480.213 / 0.2010.059 / 0.0511/160.035
#632 / 400.262 / 0.2500.073 / 0.0635/640.044
#832 / 360.312 / 0.2980.087 / 0.0773/320.052
#1024 / 320.361 / 0.3470.101 / 0.0911/80.070
1/4 in20 / 280.437 / 0.4190.132 / 0.1225/320.087
5/16 in18 / 240.547 / 0.5270.166 / 0.1523/160.105
3/8 in16 / 240.656 / 0.6360.199 / 0.1857/320.122
1/2 in13 / 200.875 / 0.8510.265 / 0.2455/160.175
5/8 in11 / 181.000 / 0.9700.331 / 0.3113/80.210

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