I'm having serious hygiene(mite) issues with the nest and dropped one of the bolts into the gutter while cleaning it - damnit

Can I know the size of the bolt used? none of the spare bolts I have in my house matched.
part missing is on the picture below.

also any advice on making ants to throw their wastes on the outworld? them stacking inside some of their empty rooms is the reason this happened in the first place
