EC34 headset standard (external cup vs ZS44 headset standard (zero stack: specs compared
Updated 05 September 2026.
2
specs differ
EC34 headset standard (external cup and ZS44 headset standard (zero stack differ on 2 specs: shis designation, cup / bearing outside diameter.
| Spec | EC34 headset standard (external cup | ZS44 headset standard (zero stack |
|---|---|---|
| SHIS designation | EC34 (external cup (EC)) | ZS44 (zero stack (ZS)) |
| Cup / bearing outside diameter | 34.0 mm cup outside diameter, 33.8 to 33.95 mm head-tube bore | 44.0 mm cup outside diameter, 43.9 to 43.95 mm head-tube bore |
| Steerer diameter | 28.6 mm (1 1/8 in) | 28.6 mm (1 1/8 in) |
| Crown race | 30.0 mm crown race seat | 30.0 mm crown race seat |
Questions and answers
How do EC34 headset standard (external cup and ZS44 headset standard (zero stack compare?
EC34 headset standard (external cup and ZS44 headset standard (zero stack differ on 2 specs: shis designation, cup / bearing outside diameter.