There are two different designs that were released for the NIPRO M1 headlight. These parts are not interchangeable. If you own a swivel mount M1 headlight than you can only replace with a swivel mount design. If you own a fixed mount M1 headlight than you can only replace with a fixed mount design.
Swivel Mount - Allows rotation of the headlight from left to right up to 360 degrees
Fixed Mount - Fixed position headlight for increased stability