# Flexible shaft couplers, 5–10 mm bores

> What size is a 5 mm to 8 mm flexible coupler?

- Category: Hardware › Motion
- Kind: Hardware
- Basis: Common aluminium helical (beam) couplers as sold for 3D printers and CNC kits
- Page: https://xemstudio.com/objects/shaft-couplers/ · JSON: https://xemstudio.com/api/geometry?object=shaft-couplers · Plain text: https://xemstudio.com/objects/shaft-couplers/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Ø19 × 25 mm for 5 → 5 and 5 → 8; Ø25 × 30 mm for 6.35/8/10 mm bores. Two set screws per end at 90°.
- Helical couplers take 0.2 mm misalignment; for a lead screw also add a bearing block at the far end or let the end float.
- Spiral cut is shown as three slots in these files; the envelope is what matters for the print.

## Sizes

| bore_1_mm | bore_2_mm | od_mm | length_mm | set_screws |
|---|---|---|---|---|
| 5 | 5 | 19 | 25 | M4 × 2 per end |
| 5 | 8 | 19 | 25 | M4 × 2 per end |
| 5 | 8 | 25 | 30 | M4 × 2 per end |
| 6.35 | 8 | 25 | 30 | M4 × 2 per end |
| 8 | 8 | 25 | 30 | M4 × 2 per end |
| 8 | 10 | 25 | 30 | M4 × 2 per end |

## Where the files are

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

## Free STEP/STL (6 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/shaft-couplers/index.json

- coupler-5x5-d19: [STEP](https://xemstudio.com/files/hardware/shaft-couplers/coupler-5x5-d19.step) · [STL](https://xemstudio.com/files/hardware/shaft-couplers/coupler-5x5-d19.stl) — flexible coupler 5 → 5 mm, Ø19 × 25; spiral shown as slots
- coupler-5x8-d19: [STEP](https://xemstudio.com/files/hardware/shaft-couplers/coupler-5x8-d19.step) · [STL](https://xemstudio.com/files/hardware/shaft-couplers/coupler-5x8-d19.stl) — flexible coupler 5 → 8 mm, Ø19 × 25; spiral shown as slots
- coupler-5x8-d25: [STEP](https://xemstudio.com/files/hardware/shaft-couplers/coupler-5x8-d25.step) · [STL](https://xemstudio.com/files/hardware/shaft-couplers/coupler-5x8-d25.stl) — flexible coupler 5 → 8 mm, Ø25 × 30; spiral shown as slots
- coupler-6.35x8-d25: [STEP](https://xemstudio.com/files/hardware/shaft-couplers/coupler-6.35x8-d25.step) · [STL](https://xemstudio.com/files/hardware/shaft-couplers/coupler-6.35x8-d25.stl) — flexible coupler 6.35 → 8 mm, Ø25 × 30; spiral shown as slots
- coupler-8x8-d25: [STEP](https://xemstudio.com/files/hardware/shaft-couplers/coupler-8x8-d25.step) · [STL](https://xemstudio.com/files/hardware/shaft-couplers/coupler-8x8-d25.stl) — flexible coupler 8 → 8 mm, Ø25 × 30; spiral shown as slots
- coupler-8x10-d25: [STEP](https://xemstudio.com/files/hardware/shaft-couplers/coupler-8x10-d25.step) · [STL](https://xemstudio.com/files/hardware/shaft-couplers/coupler-8x10-d25.stl) — flexible coupler 8 → 10 mm, Ø25 × 30; spiral shown as slots

## Questions

**What coupler connects a NEMA 17 to a T8 lead screw?**

A 5 mm → 8 mm flexible coupler, Ø19 × 25 mm (or Ø25 × 30 for more torque).

**What is the OD of a 5x8 flexible coupler?**

19 mm on the small (25 mm long) version, 25 mm on the 30 mm long version.

## Fits with

- [T8 lead screw and brass nut (Tr8×8, 2 mm pitch 4-start)](https://xemstudio.com/objects/lead-screw-t8/)
- [NEMA 17 stepper motor](https://xemstudio.com/objects/nema-17-stepper/)
- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/)
- [NEMA 8, 11, 14, 23 and 34 stepper motors](https://xemstudio.com/objects/nema-steppers-8-to-34/)