The center hole. The inner one is much bigger, big enough to go over the balancer hub. The outer pulley has a center hole only 3/4" or so in diameter. The outer one has a bunch of smaller holes around the perimeter too.
Do you have a photo of what you're talking about? I'm not quite grasping what the difference would look like on my application. Are you saying the offset is different of the pulley also? Or just the way the pulley mounts?
