Open flat belt and two pulleys (2 : 1) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/belt-and-pulleys-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 1 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- An open belt on two pulleys turns both shafts the same way; speed ratio = D₂/D₁ = 80/40 = 2 : 1 (less a little slip). Belt inside length here 471.36 mm for 140 mm centres.
- Wrap on the small pulley = 2·acos((R₂ − R₁)/C) = 163.6°: the smaller the wrap, the less torque before slipping.
- Brown's No. 1 (belt and pulleys); a crossed belt (No. 2) reverses the driven shaft.
- Parts (each has its own page): flanged-flat-pulley-40, flanged-flat-pulley-80, flat-belt-1-5x16-pulleys-40-80-140.
- Brown's movement No. 1 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
pulleys  Ø40 and Ø80, flanged
centres  140 mm
ratio  2 : 1
belt  16 × 1.5, 471.36 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. 1: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_001.html

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