# Set screws (grub screws), M3–M8 (ISO 4026)

> What size set screw holds a 5 mm shaft coupler or pulley?

- Category: Hardware › Fasteners
- Kind: Hardware
- Basis: ISO 4026 flat point, hex socket
- Page: https://xemstudio.com/objects/set-screws-metric/ · JSON: https://xemstudio.com/api/geometry?object=set-screws-metric · Plain text: https://xemstudio.com/objects/set-screws-metric/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Headless; the whole length is thread. Used to lock pulleys, couplers and collars onto shafts: use two at 90° and seat one on the shaft's D-flat.
- Hex keys: M3 1.5, M4 2, M5 2.5, M6 3, M8 4 mm. Cup and dog points exist; flat point is the common one in printer kits.

## Sizes

| thread | hex_key_mm | common_lengths_mm |
|---|---|---|
| M3 | 1.5 | 3, 4, 5, 6, 8, 10 |
| M4 | 2.0 | 4, 5, 6, 8, 10, 12 |
| M5 | 2.5 | 5, 6, 8, 10, 12 |
| M6 | 3.0 | 6, 8, 10, 12, 16 |
| M8 | 4.0 | 8, 10, 12, 16, 20 |

## Where the files are

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

## Free STEP/STL (27 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/set-screws-metric/index.json

- set-m3x3: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x3.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x3.stl) — ISO 4026 M3 × 3 flat point, 1.5 mm key
- set-m3x4: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x4.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x4.stl) — ISO 4026 M3 × 4 flat point, 1.5 mm key
- set-m3x5: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x5.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x5.stl) — ISO 4026 M3 × 5 flat point, 1.5 mm key
- set-m3x6: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x6.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x6.stl) — ISO 4026 M3 × 6 flat point, 1.5 mm key
- set-m3x8: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x8.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x8.stl) — ISO 4026 M3 × 8 flat point, 1.5 mm key
- set-m3x10: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x10.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m3x10.stl) — ISO 4026 M3 × 10 flat point, 1.5 mm key
- set-m4x4: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x4.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x4.stl) — ISO 4026 M4 × 4 flat point, 2.0 mm key
- set-m4x5: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x5.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x5.stl) — ISO 4026 M4 × 5 flat point, 2.0 mm key
- set-m4x6: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x6.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x6.stl) — ISO 4026 M4 × 6 flat point, 2.0 mm key
- set-m4x8: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x8.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x8.stl) — ISO 4026 M4 × 8 flat point, 2.0 mm key
- set-m4x10: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x10.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x10.stl) — ISO 4026 M4 × 10 flat point, 2.0 mm key
- set-m4x12: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x12.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m4x12.stl) — ISO 4026 M4 × 12 flat point, 2.0 mm key
- set-m5x5: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x5.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x5.stl) — ISO 4026 M5 × 5 flat point, 2.5 mm key
- set-m5x6: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x6.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x6.stl) — ISO 4026 M5 × 6 flat point, 2.5 mm key
- set-m5x8: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x8.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x8.stl) — ISO 4026 M5 × 8 flat point, 2.5 mm key
- set-m5x10: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x10.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x10.stl) — ISO 4026 M5 × 10 flat point, 2.5 mm key
- set-m5x12: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x12.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m5x12.stl) — ISO 4026 M5 × 12 flat point, 2.5 mm key
- set-m6x6: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x6.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x6.stl) — ISO 4026 M6 × 6 flat point, 3.0 mm key
- set-m6x8: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x8.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x8.stl) — ISO 4026 M6 × 8 flat point, 3.0 mm key
- set-m6x10: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x10.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x10.stl) — ISO 4026 M6 × 10 flat point, 3.0 mm key
- set-m6x12: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x12.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x12.stl) — ISO 4026 M6 × 12 flat point, 3.0 mm key
- set-m6x16: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x16.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m6x16.stl) — ISO 4026 M6 × 16 flat point, 3.0 mm key
- set-m8x8: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x8.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x8.stl) — ISO 4026 M8 × 8 flat point, 4.0 mm key
- set-m8x10: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x10.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x10.stl) — ISO 4026 M8 × 10 flat point, 4.0 mm key
- set-m8x12: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x12.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x12.stl) — ISO 4026 M8 × 12 flat point, 4.0 mm key
- set-m8x16: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x16.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x16.stl) — ISO 4026 M8 × 16 flat point, 4.0 mm key
- set-m8x20: [STEP](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x20.step) · [STL](https://xemstudio.com/files/hardware/set-screws-metric/set-m8x20.stl) — ISO 4026 M8 × 20 flat point, 4.0 mm key

## Questions

**What set screw do GT2 pulleys use?**

M3 × 3 or M3 × 4, two per pulley at 90°, 1.5 mm hex key.

**What size set screw for a 5 mm to 8 mm coupler?**

M4 × 5 or M4 × 6, 2 mm hex key; most aluminium couplers come with them.

## Fits with

- [GT2 timing pulleys, 16T–60T (2 mm pitch)](https://xemstudio.com/objects/gt2-pulleys/)
- [Flexible shaft couplers, 5–10 mm bores](https://xemstudio.com/objects/shaft-couplers/)
- [NEMA 17 stepper motor](https://xemstudio.com/objects/nema-17-stepper/)
- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/)