[Walt Fricke]

Any 6mm fine thread part will do. There are plugs which are just a short threaded part, like a cut off piece of a bolt, with an Allen hex for screwing them in, which make a nice clean installation. You can use a thread locker to help ,keep them in, as they don't really get torqued - just screw in until flush. Hunt around in your favorite nut and bolt seller's catalog.

Or just buy short M6 fine thread bolts with the 10mm socket heads, and install with or without a crush washer.