Alt. pulley size
 

The belt on my truck is squealing like hell with any rpms. I need to put the factory size pulley back on my 1989 f-150 5.8 a/c p/s p/b a/t serpentine drive 6 groove alt. The one on it now is too small, it was replaced with a smaller one before I got the truck, this is causing the tensioner to not be able to put the proper tension on the belt. The only info I can find is from a shop here in Houston that says it is a 58 or 62 mm. I am thinking the difference between the two will not make a difference. Any info would be appreciated. Thanks.

I would contact a salvage yard and ask them for the pulley. It will be cheaper, and work the same.