I doubt it would be m5.5?(helicoil tap) if you say your m6 bolt is in there. What I would do is grab a helicoil kit, put a helicoil in halfway through so that some of the coil is sticking out, then try and put the m5 bolt in and see whats its like. If it doesnt work and is too loose, take the bolt out, and uncoil the helicoil from the frame to get it out, using the bit coil not inserted to the frame. If it does work then still take the helicoil out and put one in properly. Well thats what Id do.