# Parallel ruler with two swinging arms (parallelogram)

> How does a two-arm parallel ruler work?

- Category: Mechanisms › Linkages
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 325 (1868)
- Page: https://xemstudio.com/objects/swinging-arm-parallel-ruler-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=swinging-arm-parallel-ruler-mechanism · Plain text: https://xemstudio.com/objects/swinging-arm-parallel-ruler-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Two straight-edges joined by two equal arms pivoted 100 mm apart on each: the four pivots always form a parallelogram, so the upper bar stays parallel to the lower one while it swings sideways and away from it.
- Drawn with the 60 mm catalog links at 60°: the upper bar is offset 30 mm along and 51.96 mm across; the opening ranges from 0 to 60 mm (arms square to the bars).
- Brown's No. 325 — the common drawing-office parallel ruler; the arms must be exactly equal and the pivot spacings identical or the bars twist.
- Parts (each has its own page): parallel-ruler-bar-200-h100, four-bar-links, dowel-pins-metric.
- Brown's movement No. 325 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| bars | 2 × 200 × 20 × 5 mm |
| arms | 2 × 60 mm (four-bar link) |
| pivot spacing | 100 mm |
| opening drawn | 51.96 mm (60°) |

## Where the files are

- Henry T. Brown (1868, public domain): [Five Hundred and Seven Mechanical Movements — scan on archive.org](https://archive.org/details/fivehundredseven00browiala) — web — Publisher's page; dimensions are facts
- 507movements.com: [Brown's movement No. 325: figure, his text and an animation](https://507movements.com/mm_325.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/swinging-arm-parallel-ruler-mechanism/index.json · license: https://xemstudio.com/files/hardware/swinging-arm-parallel-ruler-mechanism/LICENSE.md

- swinging-arm-parallel-ruler-mechanism-assembly: [STEP](https://xemstudio.com/files/hardware/swinging-arm-parallel-ruler-mechanism/swinging-arm-parallel-ruler-mechanism-assembly.step) · [STL](https://xemstudio.com/files/hardware/swinging-arm-parallel-ruler-mechanism/swinging-arm-parallel-ruler-mechanism-assembly.stl) — Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)

## Questions

**How does a two-arm parallel ruler work?**

Two straight-edges joined by two equal arms pivoted 100 mm apart on each: the four pivots always form a parallelogram, so the upper bar stays parallel to the lower one while it swings sideways and away from it.

## Fits with

- [Parallel ruler bar 200 × 20 × 5 with Ø3 pivot holes 100 mm apart](https://xemstudio.com/objects/parallel-ruler-bar-200-h100/)
- [Four-bar links: flat links with 20 to 100 mm hole centres](https://xemstudio.com/objects/four-bar-links/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)