ISO 3764:2016 specifies the types and fitting dimensions of mechanical and electromechanical watch-movements.

This International Standard is applicable to the five following types of movements:

- Type 1: round;

- Type 2: shaped round;

- Type 3: round with double cutting;

- Type 4: 5 ½′′′;

- Type 5: 6 × 8′′′.