Ratchet wheels Ø40 with 12, 24 and 36 teeth — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/ratchet-wheels/  (CC BY 4.0)
Basis: Sawtooth wheel: tips at R20, roots at R17 (3 mm deep), each tooth rising over 85 % of the pitch and dropping over 15 %
Catalog version: 2026-10-20

Sizes: see table below
- A Ø40 × 6 wheel with a Ø5 bore and 12, 24 or 36 sawtooth teeth 3 mm deep (tips on R20, roots on R17).
- Each tooth rises from root to tip over 85 % of the pitch (the back) and drops back over 15 % (the face the pawl locks against).
- Steps: 12 teeth 30°, 24 teeth 15°, 36 teeth 10°. Fewer teeth are larger and stronger.
- A one-way drive: anti-reverse on a reel, a hand-wound starter, or between a Stirling flywheel and a generator so the generator never back-drives the engine.

file  teeth  step  tip Ø  root Ø  thickness  bore
ratchet-12t-d40  12  30°  40  34  6  5
ratchet-24t-d40  24  15°  40  34  6  5
ratchet-36t-d40  36  10°  40  34  6  5

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, 3 parts): https://xemstudio.com/files/hardware/ratchet-wheels/index.json
API: https://xemstudio.com/api/geometry?object=ratchet-wheels