# Bicycle fork steerer, 1 1/8 in (28.6 mm), threadless

> What diameter is a 1 1/8 inch steerer tube?

- Category: Everyday mounts › Bicycle
- Kind: Standard part
- Basis: White Industries star nut spec (1 1/8 in = 28.6 mm steerer, M6 × 1 thread, nominal Ø26.7 × 15) and Cane Creek top cap spec (S.H.I.S. stem clamp diameter 28.6)
- Page: https://xemstudio.com/objects/bicycle-steerer-1-1-8/ · JSON: https://xemstudio.com/api/geometry?object=bicycle-steerer-1-1-8 · Plain text: https://xemstudio.com/objects/bicycle-steerer-1-1-8/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- The threadless 1 1/8 in steerer is Ø28.6 mm outside (1 1/8 in is 28.575 mm; the industry writes 28.6). The stem clamps around it, so a stem-cap or top-cap mount clamps the same Ø.
- The top cap bolt is M6 × 1 into a star nut pressed inside the steerer; White Industries gives the star nut a nominal Ø26.7 × 15. The star nut and top cap are not drawn (their fingers and caps differ by maker).
- File: the steerer as a Ø28.6 × 100 section, axis on X, plus a DXF of the circle (the outside only). Stem faceplate bolt patterns are not standardized between makers and are not drawn.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| steerer outside | Ø28.6 (1 1/8 in) | stem clamp, headset top cap | clamp | steerer-* |

## Sizes

| feature | mm | from |
|---|---|---|
| steerer outside | Ø28.6 (1 1/8 in) | White Industries, Cane Creek |
| top cap bolt | M6 × 1 | White Industries |
| star nut (nominal) | Ø26.7 × 15 | White Industries |
| stem clamp on the steerer | 28.6 | Cane Creek (S.H.I.S.) |

## Where the files are

- White Industries: [Headset star nut: 1 1/8 in (28.6 mm) steerer, M6 × 1 thread, nominal Ø26.7 × 15](https://www.whiteind.com/product/headset-star-nut/) — web — manufacturer spec (verify at link)
- Cane Creek (listing by Velomine): [Headset top cap 28.6 mm: S.H.I.S. stem clamp diameter 28.6, fits 1 1/8 in threadless](https://velomine.com/products/cane-creek-chroma-studio-headset-top-cap-28-6mm-silver) — web — reference (verify at link)

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/bicycle-steerer-1-1-8/index.json

- steerer-28.6-L100: [STEP](https://xemstudio.com/files/hardware/bicycle-steerer-1-1-8/steerer-28.6-L100.step) · [STL](https://xemstudio.com/files/hardware/bicycle-steerer-1-1-8/steerer-28.6-L100.stl) · [DXF](https://xemstudio.com/files/hardware/bicycle-steerer-1-1-8/steerer-28.6-L100.dxf) — 1 1/8 in steerer section Ø28.6 × 100 long, axis on X: the outside of the steerer (the wall is not drawn); DXF = the Ø28.6 circle

## How it fits

### Connects to
- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/): M6 top cap bolt into the star nut

### Alternatives
- [Bicycle handlebar diameters: 22.2, 23.8, 25.4, 26.0, 31.8 and 35.0 mm](https://xemstudio.com/objects/bicycle-handlebar-diameters/): mount on the bar instead of the stem

## Questions

**What diameter is a 1 1/8 steerer?**

28.6 mm outside (1 1/8 in = 28.575 mm).

**What thread is a bike top cap bolt?**

M6 × 1 into the star nut, on 1 1/8 in steerers.

**Can a mount replace the headset top cap?**

A top-cap mount takes the place of the cap under the same M6 × 1 bolt; it must still let the bolt preload the headset as the cap does.

## Fits with

- [Bicycle handlebar diameters: 22.2, 23.8, 25.4, 26.0, 31.8 and 35.0 mm](https://xemstudio.com/objects/bicycle-handlebar-diameters/)
- [Handlebar clamp rings: split rings for 22.2 to 35.0 mm bars, M4 / M5](https://xemstudio.com/objects/handlebar-clamp-rings/)
- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/)