always had a extra 12 bolt laying around. well, traded my past differential for a 350x three wheeler. So I can replace it with a 4.56 posi and a new set of 4.10s. I don't have a project to put them in, dont need it for my cars, but feel like I should get it just for general purposes. if I wasn't buying a new set of plastics for tje new trike $400 and a new seat kit for my old 185s trike ($160) I wouldn't hesitate. jim