I've just drilled a hole through the wall(or least I thought I had) anyway the hole was where there already but needed to widen it to accomadate passing a BB cable through.
Started on one side but was met with resistance so I decided to drill through from the otherside,again met with resistance but eventually got through only to find there was one and a half holes on the otherside of the wall.
Looks like someone had attempted to drill the wall(probably with a short drill bit) and was guessing the distance with an iffy tape measure. ;-)