# BBs: steel Ø4.5 mm (.177) and airsoft Ø6.0 mm

> What diameter is a BB and an airsoft BB?

- Category: Hardware › Found & household materials
- Kind: Standard part
- Basis: Steel BB .177 calibre (Ø4.5); airsoft 6 mm BB (5.95 ±0.01); drawn as true spheres
- Page: https://xemstudio.com/objects/steel-and-airsoft-bbs/ · JSON: https://xemstudio.com/api/geometry?object=steel-and-airsoft-bbs · Plain text: https://xemstudio.com/objects/steel-and-airsoft-bbs/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

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

## Notes

- A steel BB is Ø4.5 mm (.177 calibre); the file is a Ø4.5 sphere.
- An airsoft BB is nominally Ø6.0 mm, typically 5.95 ±0.01 mm; the file is a Ø6.0 sphere.
- Airsoft BBs are round enough to act as 6 mm balls in a race with a Ø6.0 groove under light load.
- On the can engine I use BBs as low-friction guides for the displacer rod.

## Sizes

| ball | dia_mm | note |
|---|---|---|
| steel BB | 4.5 | .177 cal |
| airsoft BB | 6.0 | 5.95 ±0.01 typical |

## Where the files are

- Wikipedia: [Craft stick](https://en.wikipedia.org/wiki/Craft_stick) — web — CC BY-SA 4.0 (text)
- Wikipedia: [BB gun](https://en.wikipedia.org/wiki/BB_gun) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Table tennis](https://en.wikipedia.org/wiki/Table_tennis) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds (videos and write-ups)](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/steel-and-airsoft-bbs/index.json

- steel-bb-4-5mm: [STEP](https://xemstudio.com/files/hardware/sticks-skewers-wire-bbs/steel-bb-4-5mm.step) · [STL](https://xemstudio.com/files/hardware/sticks-skewers-wire-bbs/steel-bb-4-5mm.stl) — steel BB Ø4.5 (.177 cal)
- airsoft-bb-6mm: [STEP](https://xemstudio.com/files/hardware/sticks-skewers-wire-bbs/airsoft-bb-6mm.step) · [STL](https://xemstudio.com/files/hardware/sticks-skewers-wire-bbs/airsoft-bb-6mm.stl) — airsoft BB Ø6.0 (5.95)

## How it fits

### Goes in or on
- [Can-engine cap for 53.3, 58, 66 and 76.2 mm cans](https://xemstudio.com/objects/can-engine-cap/): BBs as guides along the displacer rod

### Alternatives
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/): a ball bearing where a race of loose balls is not enough
- [Glass marbles 1/2 in, 5/8 in and Ø16 mm](https://xemstudio.com/objects/glass-marbles/): larger loose balls (Ø16)

## Questions

**What diameter is a steel BB?**

4.5 mm (.177 calibre).

**What size is an airsoft BB?**

6 mm nominal, typically 5.95 ±0.01 mm.

**Can airsoft BBs be used as bearing balls?**

For light loads, yes: they are 5.95 ±0.01 mm, so a race groove drawn at Ø6.0 holds them.

## Fits with

- [Glass marbles 1/2 in, 5/8 in and Ø16 mm](https://xemstudio.com/objects/glass-marbles/)
- [Ping-pong ball Ø40 mm, 0.4 mm wall](https://xemstudio.com/objects/ping-pong-ball/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [Can-engine cap for 53.3, 58, 66 and 76.2 mm cans](https://xemstudio.com/objects/can-engine-cap/)