Aux Belt

[RJDubya]

Its a long headed allen key bolt with a flange which pushes down onto the tensioner to push it down, tightening the bolt. I think the previous owner/garage had tried to loosen this (anticlockwise) which actually tightens it, so when i came to do it the allen key hole was round...

http://www.ebay.co.uk/itm/Alternator-Fan...5895982404

this is the tensioner mine had, there are others listed which say they are for DTs although ive never seen 1 fitted. I think later ones have the same as the hdi maybe