EC44 headset standard (external cup vs ZS44 headset standard (zero stack: specs compared
Updated 05 September 2026.
4
specs differ
EC44 headset standard (external cup and ZS44 headset standard (zero stack differ on 4 specs: shis designation, cup / bearing outside diameter, steerer diameter, crown race.
| Spec | EC44 headset standard (external cup | ZS44 headset standard (zero stack |
|---|---|---|
| SHIS designation | EC44 (external cup (EC)) | ZS44 (zero stack (ZS)) |
| Cup / bearing outside diameter | 44.0 mm cup outside diameter, about 43.9 mm head-tube bore | 44.0 mm cup outside diameter, 43.9 to 43.95 mm head-tube bore |
| Steerer diameter | 28.6 mm upper (1 1/8 in) or 38.1 mm lower (1 1/2 in) crown race | 28.6 mm (1 1/8 in) |
| Crown race | 30.0 mm upper crown race, 40.0 mm lower crown race | 30.0 mm crown race seat |
Questions and answers
How do EC44 headset standard (external cup and ZS44 headset standard (zero stack compare?
EC44 headset standard (external cup and ZS44 headset standard (zero stack differ on 4 specs: shis designation, cup / bearing outside diameter, steerer diameter, crown race.