BuiltCivic99

so i have b16A and my alternator was shot so i got a new one for a 99 civic si b16a2 and theres a problem with it fitting its something to do with the bolt and the top of the alternaor not being threaded or sometrhing like that does any1 kno what im talking about or run into this problem if i have the b16a what do i need to get an alternator from what car from auto zone or something thx...