Serpentine Belt Tensioner Stud

My '96 300tdi Disco threw its belts out of the pram on the way to work this morning. Whilst repairing and wondering "Why?" I noticed that the tensioner pulley mechanism had lots of play in it. I thought I'd just tighten the nut up but it seemed to be turning the whole stud - removal followed and on inspection it seems the stud has stripped part of the thread from the block. The stud has 2 threaded ends, 1 longer than the other it was the short end into the block but there was lots showing through the tensioner mounting, the femal thread in the block has been half stripped, so I have a couple of questions:

1. Which way round should the stud be? long thread into the block or short?
2. I'm going to get a helicoil kit to repair the thread - what size and pitch is the stud? I'm thinking M10 1.25pitch?

m10 x 1.5 short thread goes into housing ,tighten stup up with 2 nuts before fitting tensioner

Great, thanks for that.