A developing cartridge may include multiple rotary members, at least one of the rotary members configured to be detected by an image forming apparatus. In one example, the rotary members may include engagement portions configured to engage with one another to rotate the rotary members. Additionally or alternatively, in a case where one rotary member is in a driven position, the other rotary member may be rotatable a predefined amount from a non-driving state in which the other rotary member is rotatably disengaged from the one rotary member, to a driving state in which the other rotary member rotatably engages the one rotary member with the engagement portions in contact with one another.