# Lifting tongs: load-tightened scissor grip

> Why do lifting tongs grip harder with a heavier load?

- Category: Mechanisms › Linkages
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 494 (1868)
- Page: https://xemstudio.com/objects/lifting-tongs-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=lifting-tongs-mechanism · Plain text: https://xemstudio.com/objects/lifting-tongs-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 arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held.
- Drawn gripping a 40 mm block: arms crossed at ±22.02°, link holes 60 mm above and feet 80 mm below the pivot, 40 mm links to the shackle pin 88.69 mm above the pivot.
- Brown's No. 494 (lifting tongs with a shackle and links); ice tongs, log tongs and crane grabs.
- Parts (each has its own page): lifting-tong-arm-140-foot, tongs-shackle-link-50, load-block-40, four-bar-links, dowel-pins-metric.
- Brown's movement No. 494 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| arms | 2, crossed, 60 / 80 mm |
| links | 2 × 40 mm |
| load drawn | 40 mm block |
| arm angle | ±22.02° |

## 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. 494: figure, his text and an animation](https://507movements.com/mm_494.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/lifting-tongs-mechanism/index.json · license: https://xemstudio.com/files/hardware/lifting-tongs-mechanism/LICENSE.md

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

## Questions

**Why do lifting tongs grip harder with a heavier load?**

Two arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held.

## Fits with

- [Lifting tong arm 12 × 5: link hole 60 mm and foot 80 mm either side of the pivot](https://xemstudio.com/objects/lifting-tong-arm-140-foot/)
- [Tongs shackle link 50 mm centres, 12 × 5](https://xemstudio.com/objects/tongs-shackle-link-50/)
- [Block 40 × 40 × 40 (the gripped load)](https://xemstudio.com/objects/load-block-40/)
- [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/)