EC34 headset standard (external cup, 34 mm)
What a EC34 headset measures under the SHIS standard, and how to tell it apart from lookalikes.
Published dimensions
| SHIS designation | EC34 (external cup (EC)) |
|---|---|
| Cup / bearing outside diameter | 34.0 mm cup outside diameter, 33.8 to 33.95 mm head-tube bore |
| Steerer diameter | 28.6 mm (1 1/8 in) |
| Crown race | 30.0 mm crown race seat |
Used on: the standard 1 1/8 in external-cup upper or lower on older road and rigid frames.
EC34 is the classic 1 1/8 in external cup: the bearing sits in a cup pressed outside the head tube, so the head-tube bore is only 33.8 to 33.95 mm. It is not interchangeable with the 44 mm EC44 or ZS44 bores even though both take a 28.6 mm steerer.
Frames and related headsets
EC44external cup, 44 mmEC49external cup, 49.6 mmZS44zero stack, 44 mmZS55zero stack, 55 mmIS41integrated, 41 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