Socket head cap screw

ISO 4762 / DIN 912 (ASME B18.3 in inch sizes)

Sizes

M1.6-M64 metric; #0 to 3/4 in UNC/UNF

Drive & head

Internal hex (Allen key), tall cylindrical head

Materials

Alloy steel, A2/A4 stainless, titanium

Strength / grades

8.8, 10.9, 12.9 steel; A2-70 / A4-80 stainless

Hole and pilot guidance

Clearance hole about 1.1x the thread size (M6 = 6.6 mm close fit, 7 mm normal). Counterbore must be wider than the head.

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Machine tools, jigs and fixtures

Strong head lets the screw sit in a counterbored pocket with a small footprint

3D printers and robotics frames

Fits the recessed slots and pockets of aluminium extrusion

The tall head needs depth - it will not sit flush under a thin panel.
You need straight-line room for the hex key, not just for the screw.
A counterbore that is too small makes the head bind and gives a false tight feeling.