You'll need a heli-coil kit. I got some engineer to do mine, as I didn't trust myself. You need to drill the holes slightly bigger, then insert the thread with the heli-coil tool, like, one full turn, the half back, then full turn, half back...etc. And yeah, then just bosh out the bottom of the heli-coil, and you're sorted. Just make sure it's drilled, and fitted perfexctly straight.