IS41 headset standard (integrated, 41 mm)
What a IS41 headset measures under the SHIS standard, and how to tell it apart from lookalikes.
Published dimensions
| SHIS designation | IS41 (integrated (IS)) |
|---|---|
| Cup / bearing outside diameter | 41.0 to 41.1 mm bearing outside diameter |
| Steerer diameter | 28.6 mm (1 1/8 in) |
| Crown race | 30.0 mm crown race, or machined into the fork |
Used on: the common 1 1/8 in integrated upper: the bearing drops straight into a 41 mm seat in the head tube.
IS41 is a true integrated headset: the cartridge bearing sits directly in a 41.0 to 41.1 mm angled seat in the carbon head tube with no pressed cup. It is not the same as ZS44, which uses a pressed cup in a 44 mm bore.
Frames and related headsets
EC34external cup, 34 mmEC44external cup, 44 mmEC49external cup, 49.6 mmZS44zero stack, 44 mmZS55zero stack, 55 mmBSA bottom bracket shellthe frame's other threaded interface
SOURCES: Park Tool, Standardized Headset Identification System (SHIS) · Cane Creek et al., Standardized Headset Identification System [SHIS] specification