Bicycle fork steerer, 1 1/8 in (28.6 mm), threadless — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/bicycle-steerer-1-1-8/  (CC BY 4.0)
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)
Catalog version: 2026-10-20

Sizes: see table below
- 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.

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.)

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- White Industries: Headset star nut: 1 1/8 in (28.6 mm) steerer, M6 × 1 thread, nominal Ø26.7 × 15 — web — manufacturer spec [verify license at link] — https://www.whiteind.com/product/headset-star-nut/
- 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 — web — reference [verify license at link] — https://velomine.com/products/cane-creek-chroma-studio-headset-top-cap-28-6mm-silver

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/bicycle-steerer-1-1-8/index.json
API: https://xemstudio.com/api/geometry?object=bicycle-steerer-1-1-8