# Flat washers, M2–M8 (ISO 7089)

> What are the dimensions of M3, M4 and M5 flat washers?

- Category: Hardware › Fasteners
- Kind: Hardware
- Basis: ISO 7089 (normal series)
- Page: https://xemstudio.com/objects/flat-washers-metric/ · JSON: https://xemstudio.com/api/geometry?object=flat-washers-metric · Plain text: https://xemstudio.com/objects/flat-washers-metric/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Inner diameter clears the screw; outer diameter is what a counterbore has to accommodate if the washer sits in it.

## Sizes

| thread | id_mm | od_mm | thickness_mm |
|---|---|---|---|
| M2 | 2.2 | 5 | 0.3 |
| M2.5 | 2.7 | 6 | 0.5 |
| M3 | 3.2 | 7 | 0.5 |
| M4 | 4.3 | 9 | 0.8 |
| M5 | 5.3 | 10 | 1 |
| M6 | 6.4 | 12 | 1.6 |
| M8 | 8.4 | 16 | 1.6 |

## Where the files are

- McMaster-Carr: [Washers (free STEP/IGES/STL per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/washers/) — STEP, IGES, STL, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)
- Wikipedia: [Washer (hardware)](https://en.wikipedia.org/wiki/Washer_(hardware)) — web — CC BY-SA 4.0 (text)

## Free STEP/STL (7 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/flat-washers-metric/index.json

- washer-m2: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m2.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m2.stl) — ISO 7089 M2
- washer-m2.5: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m2.5.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m2.5.stl) — ISO 7089 M2.5
- washer-m3: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m3.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m3.stl) — ISO 7089 M3
- washer-m4: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m4.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m4.stl) — ISO 7089 M4
- washer-m5: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m5.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m5.stl) — ISO 7089 M5
- washer-m6: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m6.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m6.stl) — ISO 7089 M6
- washer-m8: [STEP](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m8.step) · [STL](https://xemstudio.com/files/hardware/flat-washers-metric/washer-m8.stl) — ISO 7089 M8

## Questions

**What is the outer diameter of an M3 washer?**

7 mm OD, 3.2 mm ID, 0.5 mm thick (ISO 7089). M4: 9 mm OD; M5: 10 mm OD; M6: 12 mm OD; M8: 16 mm OD.

**Do I need a washer under a screw head in a 3D print?**

Yes for soft plastics or slotted holes: it spreads the load and stops the head sinking in. Size the counterbore to the washer OD, not the head.

## Fits with

- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/)
- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/)