Drum unit, cartridge and coupling member

A developing cartridge comprising:

• a casing having a first end and a second end opposite to the first end;
• a developing roller rotatably supported by the casing;
• and
• a coupling member provided adjacent to the first end of the casing, the coupling member being operatively connected to the developing roller, the coupling member being rotatable about a rotational axis thereof, and the coupling member including (i) a cylindrical portion, (ii) a first projection at least partially positioned inside of the cylindrical portion, (iii) a second projection at least partially positioned inside of the cylindrical portion, (iv) an elastically movable projection at least partially positioned inside of the cylindrical portion, and (v) a wall extending in a direction perpendicular to the rotational axis and positioned between the second end of the casing and the first and second projections,
• wherein, along a line perpendicular to the rotational axis of the coupling member, the first projection is open to the rotational axis of the coupling member, and
• wherein, along a line perpendicular to the rotational axis of the coupling member, the second projection is open to the rotational axis of the coupling member.