Current Projects chat and miscellany

I just fitted a new BB (buddery smoov) and tried to fit a new rear derailleur.
BUT, (and there's always a fucking but with this bike) the bolt that attaches the derailleur to the hanger is too short.

Well, I think it is. What happens is that I screw the bolt in to the hanger, and it gets tighter and tighter until all of a sudden it just slackens off again. I think there isn't enough thread on either the bolt or the hanger. Would trying another mech tell me which the problem is...?

Perhaps stupid question, but are you sure you have the derailleur aligned properly on the face of the hanger? There is a adjusting screw next to the bolt that controls the tension of the derailleur, and it sits onto a protrusion on the side of the hanger. If you don't align these before you locate the bolt in the hole, it won't work..