An image forming apparatus cartridge includes a casing including an opening and an arc-shaped protrusion that is adjacent to the opening. The image forming apparatus cartridge also includes a developer roller having an axis L1 and a coupling member having an axis L2. The coupling member includes (i) a first end portion operatively connected with the developer roller, (ii) a second end portion including at least one projection that is open to the axis L2, and (iii) a connecting portion connecting the first end portion and the second end portion. A maximum distance as measured from the axis L2, in a direction perpendicular to the axis L2, of at least part of the connecting portion is shorter than a distance between the at least one projection and the axis L2.