Ratchet wheels and pawl (anti-reverse / one-way drive) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/ratchet-and-pawl/  (CC BY 4.0)
Basis: Sawtooth ratchet: tooth depth 3 mm, 85/15 flank split; pawl pivot 3 mm; dimensions chosen for printing at 0.4 mm nozzle
Catalog version: 2026-10-20

Sizes: see table below
- Ratchet tooth: the drive face is radial, the back face slopes; the pawl must contact the drive face at or below the tooth tip so load pushes it deeper, not out. Pivot the pawl so its contact point trails the pivot by 10–15°.
- 12 teeth = 30° steps (coarse, strong); 24 = 15°; 36 = 10°. Spring: a printed cantilever or a 0.5 mm music-wire torsion spring on the pivot.
- Where it goes: fishing-reel style anti-reverse, hand-wound starters, a one-way drive between a Stirling flywheel and a generator so the generator never back-drives the engine.

part  teeth  step_deg  od_mm  bore_mm
ratchet-12t  12  30  40  5
ratchet-24t  24  15  40  5
ratchet-36t  36  10  40  5
pawl-24  —  —  24 long  3.2

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Ratchet (device) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Ratchet_(device)
- Wikipedia: Pawl — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Pawl
- Long Earth Society: Engine builds that use these parts (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/ratchet-and-pawl/index.json
API: https://xemstudio.com/api/geometry?object=ratchet-and-pawl