Set screws (grub screws), M3–M8 (ISO 4026) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/set-screws-metric/  (CC BY 4.0)
Basis: ISO 4026 flat point, hex socket
Catalog version: 2026-10-20

Sizes: see table below
- Headless; the whole length is thread. Used to lock pulleys, couplers and collars onto shafts: use two at 90° and seat one on the shaft's D-flat.
- Hex keys: M3 1.5, M4 2, M5 2.5, M6 3, M8 4 mm. Cup and dog points exist; flat point is the common one in printer kits.

thread  hex_key_mm  common_lengths_mm
M3  1.5  3, 4, 5, 6, 8, 10
M4  2.0  4, 5, 6, 8, 10, 12
M5  2.5  5, 6, 8, 10, 12
M6  3.0  6, 8, 10, 12, 16
M8  4.0  8, 10, 12, 16, 20

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- McMaster-Carr: Socket head 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/socket-head-screws/
- Wikipedia: Screw — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Screw

Free files (CC BY 4.0, Xem Studio; STEP + STL, 27 parts): https://xemstudio.com/files/hardware/set-screws-metric/index.json
API: https://xemstudio.com/api/geometry?object=set-screws-metric