US Patent 10209670 Rotational force transmitting part

An electrophotographic photosensitive drum unit usable in a process cartridge includes a cylinder having a photosensitive layer at an outer periphery thereof and an axis L1. A drum flange is provided at one end of the cylinder, with the drum flange including a recess formed on an inside thereof and a gear portion provided along an outer surface of the drum flange. A detachable member is detachably attached to the drum flange and overlaps parts of the recess as seen along a direction of the axis L1, with the detachable member being provided within the drum flange in the direction of the axis L1.