Anyone know the size washer required for the side drain bolts?

Noticed a weep, AFTER I hit the front brake and got nothing!

The ID/OD is the measuement I'd like, or if you know the bolt size.

Thanks.

The bolt has a 6mm thread with a 10mm hex head. The washer usually sits flush with the bolt head, so as a guess I'd say the OD would be 10mm.
SO a 6 x 10 copper washer.

Thank you.

On my 2008 model the drain bolt threads had some rubbery seal, like thread tape. The service manual doesn't mention it and I've always wondered what I should replace it with (had to remove to clean the other crap that was stuck to it).