Screw and bolt types
The same M3 thread comes in a dozen different heads, and picking the wrong one is how panels end up not sitting flush, sockets round out and threads strip. Here is what each type is, the standard it is made to, and where it belongs.
Socket head cap screwISO 4762 / DIN 912 (ASME B18.3 in inch sizes)M1.6-M64 metric; #0 to 3/4 in UNC/UNFButton head screwISO 7380 (ISO 7380-2 adds a flange)M3-M20Countersunk (flat head) screwISO 10642 (hex), DIN 965 (Phillips), DIN 963 (slotted)M2-M20Set screw / grub screwDIN 913 flat point, 914 cone, 915 dog point, 916 cup pointM1.6-M24Shoulder bolt (stripper bolt)ISO 7379Shoulder diameters roughly 3-25 mm with a smaller thread belowHex head boltISO 4014 / DIN 931 partly threaded, ISO 4017 / DIN 933 fully threadedM1.6-M64ThumbscrewDIN 464 knurled head, DIN 465 wing head (no single master standard)M3-M10 typicalCaptive panel screwManufacturer specific - PEM PF11/PF12/PF15, Southco (no ISO/DIN)M2-M6 and #2-56 to 1/4-20Standoff / spacerNo single standard - vendor ranges (Keystone, Wurth, Essentra)M2-M6 in electronics; lengths from about 3 mm to 100 mmSEMS screw (captive washer)ASME B18.13; regional DIN washer combinationsM2-M8 metric, #2 to 3/8 inWood screwASME B18.6.1; DIN 95/97 historic, now mostly maker specsGauge #2-#20, lengths 12 mm to 150 mmDrywall screwASTM C1002#6 and #8 gauge, 25 mm to 75 mm longThread repair insert (Heli-Coil)Maker standard; dimensions align with NASM8846 and ANSI B18.29.1M2-M39 metric, #0-80 upward in inch; length usually 1x to 3x the thread sizeSecurity screw (pin-in-Torx and friends)No formal standard - security drives built onto normal heads (ISO 7045, DIN 965 etc.)M2-M10 metric, #4 to 3/8 in
Need a size instead of a type? Browse M1.2–M6 machine screws or self-tapping sizes.