How do you know what size pulley I have on my supercharger? There is no numbers on it like i've seen on others. Where do you measure? I have a dial calipers and I measured the area where the belt runs on the grooves and measures in the area of 2.8 to 2.9, so is that the size?

 

Yes, I Know they make both. if you measure the top of the grooves instead of the "valleys" that will be the size you have, thats how mine worked out.