Developing cartridge including protrusion positioned at outer surface of casing

A developing cartridge comprising:

• a developing roller extending in a first direction;
• a casing configured to accommodate a developer therein, the casing having a first outer surface and a second outer surface spaced apart from the first outer surface in the first direction, the casing having one end portion and another end portion spaced apart from the one end portion in a second direction crossing the first direction, the developing roller being positioned at the one end portion;
• an agitator rotatable about an agitator axis extending in the first direction;
• an agitator gear mounted to the agitator and rotatable with the agitator about the agitator axis, the agitator gear being positioned at the first outer surface, the agitator gear including a first gear part and a second gear part positioned between the first outer surface and the first gear part in the first direction, a first diameter of the first gear part being larger than a second diameter of the second gear part;
• a detection gear meshing with the second gear part of the agitator gear, the detection gear being rotatable about a detection axis extending in the first direction, the detection gear being positioned at the first outer surface;
• and
• a protrusion extending in the first direction, the protrusion being positioned at the first outer surface, a part of the protrusion being positioned between the first outer surface and the first gear part in the first direction,
• wherein the protrusion is positioned closer to the developing roller than the second gear part of the agitator and the detection gear in the second direction, and
• wherein the detection gear is farther from the developing roller than the protrusion is from the developing roller in the second direction.