Mainly the 4.5mm one, I have stripped three of them now. The 3.8mm cheap ones seem to hold up (only because the screws are so short that they remove.)
So I’m looking for some game Tec. quality game bits. I had a talk with the owner of a PnT and he showed me the bit that he had and it was made out of hardened steel (or just a hard metal) and not the malleable metal that the cheap ones are. I asked where he got it and if he could get me one (it was a while ago but I think) he told me he got it from the main PnT and sadly he couldn’t get me one. So I know that they are out there but I don’t know where to get one.