Parallel ruler with crossed arms and slots — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/parallel-ruler-crossed-arms-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 324 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- Two straight-edges joined by two equal crossed arms pinned at their middles; each arm is pinned to one blade and slides in a slot of the other. The pinned ends are always one above the other, so the blades stay parallel and square to each other at any opening.
- Built from two 200 mm blades and two 80 mm centre-hole links: drawn open 40 mm; the slot lets it open from 0 to 55 mm.
- Brown's No. 324 (compound parallel ruler, crossed arms with slot-and-pin).
- Parts (each has its own page): parallel-ruler-blade-200, centre-hole-link-80, dowel-pins-metric.
- Brown's movement No. 324 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
blades  2 × 200 × 20 × 5 mm
arms  2 × 80 mm, crossed at the middle
opening  0–55 mm (drawn 40)

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. 324: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_324.html

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