Helical gear, normal module 1.5, 20 teeth, helix 20° right hand, face 12, Ø6 bore — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/helical-gear-mn1-5-20t-beta20-rh-bore6/  (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 34.93, width 34.93, height 12.0
- Normal module 1.5, helix angle 20°: transverse module 1.6, transverse pressure angle 21.17°, pitch Ø31.93, tip Ø34.93, root Ø28.18; addendum 1.5, dedendum 1.88 (normal-module depths).
- The transverse involute is twisted 15.68° over the 12 mm face (lead π·d / tan β = 275.56 mm). Meshes with a 30-tooth gear of the opposite hand on a parallel shaft.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

dimension  value
normal module  1.5
teeth  20
helix angle  20° RH
transverse module  1.6
pitch Ø  31.93 mm
tip Ø  34.93 mm
face  12 mm
bore  Ø6

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. 40: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_040.html
- Xem Studio: drawing — web — Publisher's page; dimensions are facts — https://xemstudio.com/objects/helical-gears-mechanism/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/helical-gear-mn1-5-20t-beta20-rh-bore6/index.json
API: https://xemstudio.com/api/geometry?object=helical-gear-mn1-5-20t-beta20-rh-bore6