Does anyone know what size the bolts connecting the arm bracket to the vents are?

I am missing one and would like to cure the resulting rattle (I’m doing it one at a time).

I have tried a m5 and that’s too big and the m4 just falls straight out. I ordered what I thought was a vent bolt from John Craddock but what arrived was way too big.

I am sure I am missing something simple as always.

3/16" I think ....

Thanks. That would make sense. I will pick one up.