Alternator Pulley Alignment

I am having major problems with my alternator pulley to line up properly. The original one that was on there was going through a belt a week. I bought a new alternator pulley and it looked totally different. It said:
Product Notes: 30mm Extension Converts AL---X to AL---M type alternators.
I have no clue what this means, please help. Is there something else I need to do??

I've been there. My car was always eating the alternator belts all because 1 shop lost my original pulley and the one that came on the rebuilt alternator was garbage. I have no idea what alx/alm refers to. Best bet go to a junkyard and pull an original pulley (or the whole alternator with brackets) and see what's what.