Previous owner took the alternator belt tensioner out. I "acquired" the bolt, but now I've found there is nothing to thread the bolt in to. Is there another part I'm missing from the alternator?

 

There are two 10mm bolts in the front plate. One bolts to the alternator the other("special") goes down towards the engine...towards the other end of that bolt there's a bolt that runs 90 degrees through it from the left through that bolt, through the alternator and is held by a one inch long nut on the right side. You tighten the second bolt that I alluded to(labeled "special") to tighten the belt. It will draw the alternator tighter and tighter towards you, which tightens the belt.

 

Thanks! Looks like I'll be heading back to the yard.