Round-groove pulleys and round band, 1 : 1 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/round-groove-pulleys-round-band-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 257 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- The band's section matches the groove, so it is held on half its circumference and cannot ride off; it drives by friction on the groove's surface, like a flat belt but steerable round guide pulleys at any angle.
- Two equal pulleys 100 mm apart on Ø8 shafts and a Ø5 endless band, drawn seated in both grooves (band centre radius 20 mm).
- Brown's No. 257.
- Parts (each has its own page): round-groove-pulley-40-band5-bore8, round-band-5-c100-pulleys-40, linear-shafts-h6.
- Brown's movement No. 257 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
pulleys  2 × Ø40 × 10 for a Ø5 round band
band  Ø5 round
centre distance  100 mm
ratio  1 : 1

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. 257: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_257.html

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