Notched roller Ø18 × 4, Ø3 bore, 24 V-notches — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/notched-roller-d18x4-b3/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown's figure (1868); true size, no printing allowance
Catalog version: 2026-10-20

Overall (mm): length 17.93, width 17.93, height 4.0
- Ø18 × 4 roller with 24 V-notches 0.85 mm deep round its rim (they grip the paper so the ruler rolls without slipping) and a Ø3 bore; two on one axle make the ruler roll parallel to itself.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

dimension  value
diameter  18 mm
width  4 mm
notches  24 × 0.85 mm deep, 90°
bore  Ø3

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. 323: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_323.html
- Xem Studio: drawing — web — Publisher's page; dimensions are facts — https://xemstudio.com/objects/rolling-parallel-ruler-mechanism/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/notched-roller-d18x4-b3/index.json
API: https://xemstudio.com/api/geometry?object=notched-roller-d18x4-b3