EC-4 cranks are narrow fit for road/gravel ebikes, compatible with the following motors which use a steel ISIS spline:
- Brose Mag
- Fazua-R50
- TQ-HPR50
- Giant E+ System BBSS (Hub Motor) 

Not compatible with e-mountain bikes as these arms have a narrow fitment. 
Not compatible with Specialized Levo/Kenevo/Vomo/Vado. 
GUIDESECrank Fitment Guide: