Internal gear and pinion, 60 : 20 (3 : 1, same direction) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/internal-gear-and-pinion-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 34 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A pinion meshing inside a ring gear: both turn the same way (an external pair reverses), the ratio is 60 : 20 = 3 : 1, and the centres are only m(N_ring − N_pinion)/2 = 20 mm apart — a compact reduction.
- More teeth are in contact than in an external pair of the same size (the concave ring wraps the pinion), so it carries more load, as Brown notes.
- Module 1, 20°; the ring's spaces are the exact involute tooth of a 60-tooth gear; no backlash drawn.
- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1.
- Brown's movement No. 34 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
ring  60 T internal, Ø80
pinion  20 T
ratio  3 : 1, same direction
centre distance  20 mm

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala
- 507movements.com: Brown's movement No. 34: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_034.html

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/internal-gear-and-pinion-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=internal-gear-and-pinion-mechanism