EC49 headset standard (external cup vs ZS55 headset standard (zero stack: specs compared
Updated 05 September 2026.
2
specs differ
EC49 headset standard (external cup and ZS55 headset standard (zero stack differ on 2 specs: shis designation, cup / bearing outside diameter.
| Spec | EC49 headset standard (external cup | ZS55 headset standard (zero stack |
|---|---|---|
| SHIS designation | EC49 (external cup (EC)) | ZS55 (zero stack (ZS)) |
| Cup / bearing outside diameter | 49.6 to 49.7 mm cup outside diameter | 55.0 mm cup outside diameter, 54.9 to 54.95 mm head-tube bore |
| Steerer diameter | 38.1 mm (1 1/2 in) | 38.1 mm (1 1/2 in) |
| Crown race | 40.0 mm crown race seat | 40.0 mm crown race seat |
Questions and answers
How do EC49 headset standard (external cup and ZS55 headset standard (zero stack compare?
EC49 headset standard (external cup and ZS55 headset standard (zero stack differ on 2 specs: shis designation, cup / bearing outside diameter.