My mate bought new bars and stem but he didn’t have torx keys, so he brought it up to mine. One side came of easy and the other just stripped the head with hardly any force applied. So I had to drill the bolt out, which worked. Only to find the bolts must have been captured in the clamp, because the right size bolt (M5 I believe it was) threaded into the top and bottom of the clamp. So I had to drill that hole out too!
Stupid in my opinion, why didn’t they put decent bolts in them in the first place. Especially if there going to be captured in the clamp, making them non-replaceable without a drill.