I have a smaller pulley, been trying to figure out what belt to get, or really where i can find one locally. now im looking at idler pulleys, a 3.5" is offered. it looks to be the smooth pulley. well i measured my smooth idler and it is 3.5" my ribbed one is 3" along with the tensioner pulley.

so did the previous owner put on a 3.5" already? or am i looking at the wrong pulley. it seems to have a torx head bolt instead of a normal 15mm bolt

WBody store states that it is a 15mm bolt, all my other pulleys are a 15mm bolt but this one