Its called a Bendix Anders, I remember when I was a kid and my dad was fixing a starter and the motor was fine but he was replacing what he called a bendix that had a striped gear. I think thats one of the earliest mechanical jobs I helped him with and helped get me into cars. Named after the inventor I believe. I was looking at my starter and decided it was cheap on RockAuto and just bought a rebuilt instead of messing with mine. Never seen the insides of one, I've learned something, cool.