Spur gear pair, module 1, 20 : 40 teeth (2 : 1) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/spur-gear-pair-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 24 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- Two involute spur gears on parallel shafts: the speed ratio is the inverse tooth ratio (20 : 40 → output at half speed, double torque) and the shafts turn in opposite directions.
- Module 1, 20° pressure angle, centre distance m(N₁ + N₂)/2 = 30 mm exactly; teeth meet on the pitch line with no backlash drawn.
- Brown's figure 24 is the plain spur pair, the base of every gear train in the book.
- Parts (each has its own page): spur-gears-module-1.
- Brown's movement No. 24 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
module  1
teeth  20 / 40
ratio  2 : 1
centre distance  30 mm
face width  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. 24: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_024.html

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