Alternator line up

by the way, it seems odd that the grooves on the aluminum pulleys are spaced so far apart (1/4 inch?), when the factory pulley you are trying to align with they are butted right up against each other. Does the pulley manufacturer offer to revised alternator pulley with the same configuration? how far apart are the centers of the grooves on the aluminum pulleys? I think that the factory distance on a double groove pulley is 1/2 inch.