Machine screws

Machine screws have a uniform thread along their full length and a blunt tip — they do not self-thread. They require a pre-tapped hole or a nut. Used in electronics, appliances, and mechanical assemblies.

How to read a machine screw spec

Imperial: #8-32 × 1/2" = screw number (#8), threads per inch (32), length (1/2"). Metric: M5 × 0.8 × 20 = major diameter (5mm), thread pitch in mm (0.8), length (20mm).

Common imperial (UNC) sizes

Designation	Major dia.	Threads/inch	Common use
#4-40	2.8 mm	40	Small electronics, computer fans
#6-32	3.5 mm	32	PC case screws (3.5" drives), electrical panels
#8-32	4.2 mm	32	General electronics, junction boxes
#10-24	4.8 mm	24	Structural electronics, equipment racks
#10-32	4.8 mm	32	Server racks (EIA 310), instrument panels

Common metric sizes

Designation	Diameter	Thread pitch	Common use
M3 × 0.5	3.0 mm	0.5 mm	Small electronics, fans, optics
M4 × 0.7	4.0 mm	0.7 mm	Electrical equipment, brackets
M5 × 0.8	5.0 mm	0.8 mm	General mechanical assemblies
M6 × 1.0	6.0 mm	1.0 mm	Automotive trim, appliances
M8 × 1.25	8.0 mm	1.25 mm	Structural assemblies, furniture

Head styles

Head	Description
Flat (countersunk)	82° or 90° angle; sits flush after countersinking
Pan	Low profile, slightly rounded; most common
Hex (bolt head)	External hex; requires wrench, high torque
Truss	Extra-wide low-profile; good bearing surface distribution
Round (cheese)	High cylindrical head; older electronic equipment

Drive types

Phillips — #1 for M3/#4, #2 for M5/#8, most common
Slotted — single slot; older equipment and high-voltage panels where a grounded screwdriver is required
Hex socket (Allen) — high torque, tamper-resistant; very common in metric sizes
Torx — T10–T25 for small machine screws; used in consumer electronics and automotive trim

Machine screw assortments
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