Two speeds from two belts on fast and loose pulleys — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/fast-and-loose-pulleys-two-speed-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 60 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- The upper shaft carries a wide Ø80 and a wide Ø40 pulley; each drives its own belt. Below, each belt can run on a fast pulley (keyed to the shaft) or on a loose one beside it (free to turn). With belt 1 on its fast Ø40 the lower shaft runs at 2 × upper speed; shift belt 1 to its loose pulley and belt 2 onto its fast Ø80 and it runs at 0.5 ×.
- Drawn in the fast (2 : 1) setting: belt 1 on the fast Ø40, belt 2 idling on the loose Ø80. Both belts are the same length, 471.36 mm (Ø40 + Ø80 at 140 mm). Pulleys plain (no flanges) so the belts can be shifted; upper faces 34 mm wide for both positions.
- Brown's No. 60. Only one belt may be on a fast pulley at a time.
- Parts (each has its own page): plain-flat-pulley-80x34, plain-flat-pulley-40x34, plain-flat-pulley-40x16, plain-flat-pulley-80x16, flat-belt-16x1-5-pulleys-40-80-c140-open, linear-shafts-h6.
- Brown's movement No. 60 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
upper pulleys  Ø80 × 34 and Ø40 × 34 (fast)
lower pulleys  Ø40 fast + loose, Ø80 loose + fast, × 16
speeds  2 : 1 and 1 : 2
belts  2 × 16 × 1.5, 471.36 mm
shafts  Ø8, 140 mm apart

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. 60: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_060.html

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/fast-and-loose-pulleys-two-speed-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=fast-and-loose-pulleys-two-speed-mechanism