Oblong endless rack, module 1: two 4π racks joined by 20-tooth half-gear ends — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/oblong-endless-rack-m1-20t-ends/  (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 34.56, width 22.0, height 8.0
- Closed toothed outline: two straight module 1 racks 12.57 mm long (4 pitches) joined by the two halves of a 20-tooth gear, so a pinion can roll right round it; 8 mm thick, Ø3.4 centre hole. Tooth pitch is continuous (π mm on the straights, 18° on the ends) because the end radius is the gear's pitch radius, 10 mm.
- The pinion's centre runs on the parallel curve 10 mm outside the pitch line; at each end the pinion changes sides, so the rack's direction reverses while the pinion keeps turning the same way.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

dimension  value
module  1
straights  12.57 mm (4 pitches)
end radius (pitch)  10 mm
teeth on each end  10
thickness  8 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. 119: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_119.html
- Xem Studio: drawing — web — Publisher's page; dimensions are facts — https://xemstudio.com/objects/mangle-rack-oblong-mechanism/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/oblong-endless-rack-m1-20t-ends/index.json
API: https://xemstudio.com/api/geometry?object=oblong-endless-rack-m1-20t-ends