Bell cranks: 30 × 30 and 20 × 40 mm arms at 90° — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/bell-cranks/  (CC BY 4.0)
Basis: Bell crank lever: output motion = input × (output arm / input arm); 90° between arms; Ø10 pivot pocket for a 623 bearing
Catalog version: 2026-10-20

Sizes: see table below
- Turns a push or pull through 90°. The 30 × 30 crank keeps the same travel; the 20 × 40 doubles it (or halves it, driven the other way).
- Pivot is a Ø10 pocket for a 623 bearing (OD 10); arm ends have Ø3 holes for pins and links.
- Used in the beta Stirling bell-crank drive to phase the displacer and piston.

arms  angle  ratio  pivot
30 × 30 mm  90°  1:1  Ø10 (623)
20 × 40 mm  90°  1:2  Ø10 (623)

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Bellcrank — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Bellcrank
- Long Earth Society: Engine and rig builds on extrusion frames — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/bell-cranks/index.json
API: https://xemstudio.com/api/geometry?object=bell-cranks