Mine’s gone missing.

I’m not talking about the 8mm hex key, the outer bit with the 4 holes in it. I assumed it would bit a pretty loose thing you could screw in with the end of cir-clip pliers or something, after all, mine fell out, but trying my mates they’re pretty tight in there.

Should be (very) threadlocked in, that’ll be why they’re hard to remove. You’ll be able to get the new one in using a pin spanner and a load of loctite

I’ve used a Park Tool pin spanner (SPA2), but that’s not ideal. I’m guessing there’s a rigid spanner out there with fixed pin positions that makes it a breeze.

Oh, and it has a reverse screw IIRC – righty loosey, lefty tighty.