Any question answered...

I have no idea where the drum bits went, so it might take a while. And also you should totally not trust me. but I did both GCSE and A level physics only a little bit more than 10 years ago so I totally know your substitute washer will be fine.

Have you considered asking an engineer?

I don't trust any of the engineers I know, especially myself.

I'm going to attack some M10 washers tonight with a 12mm drill bit. Just need to figure out how to restrain it.