Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/imperial-machine-screws/  (CC BY 4.0)
Basis: ASME B18.6.3 / B18.3; Unified thread standard
Catalog version: 2026-10-20

Sizes: see table below
- Major diameters: #4 2.845 mm (0.112 in), #6 3.505 mm (0.138 in), #8 4.166 mm (0.164 in), 1/4 6.35 mm.
- Socket head: head dia ≈ 1.5 × major, head height = major. 1/4-20 SHCS: 0.375 in head, 0.25 in tall, 3/16 in hex key.

size  major_mm  tpi  clearance_mm  tap_drill_mm
#4-40  2.845  40  3.3  2.26
#6-32  3.505  32  3.9  2.7
#8-32  4.166  32  4.5  3.45
1/4-20  6.35  20  6.8  5.11

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- McMaster-Carr: Machine screws (free STEP/IGES/STL per part, for your own design use; no redistribution) — STEP, IGES, STL, PDF — McMaster-Carr site terms: personal design use, no redistribution [verify license at link] — https://www.mcmaster.com/products/screws/machine-screws/
- Wikipedia: Unified Thread Standard — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Unified_Thread_Standard

Free files (CC BY 4.0, Xem Studio; STEP + STL, 18 parts): https://xemstudio.com/files/hardware/imperial-machine-screws/index.json
API: https://xemstudio.com/api/geometry?object=imperial-machine-screws