Dull one this: I've managed to **** up the thread in a chain tensioner screw hole. Obviously I need to drill it out, tap it and put an insert in but I need advice on what size I need to drill in order to recreate the same bore. It was originally an 8mm hole. What size do I need to make it in order to take an 8mm helicoil insert? I assume about .5 of a mm bigger? Thoughts would be appreciated and also any advice from those that have done this before in terms of potential issues. I've tapped before but I've never had to repair an existing thread.