Cartridge, drum unit and image forming apparatus

A cartridge comprising:

• a photosensitive drum;
• a casing having a first end portion and a second end portion opposite the first end portion in an axial direction of the photosensitive drum, the casing rotatably supporting the photosensitive drum;
• and
• a coupling positioned adjacent to the first end portion of the casing, the coupling being operatively connected to the photosensitive drum so as to be capable of transmitting a driving force toward the photosensitive drum,
• wherein the coupling includes:
• a main body,
• a movable portion movable relative to the main body of the coupling between a first position and a second position, with the movable portion being closer to the second end portion of the casing in the axial direction of the photosensitive drum when the movable portion is in the second position than when the movable portion is in the first position, and
• a projection configured to move away from an axis of the coupling and relative to the main body of the coupling in response to movement of the movable portion from the first position to the second position.