I expect someone has been here before but I have worked up a table to show possible solutions to representing metric fasteners at 1/6 scale. I have personally found that BA bolts offer a close approximation, as shown in the attached table, although the head thickness tends to be very slightly over scale. Depending on the situation this may not be a an issue.
By way of illustration below are some images of a Panzer II engine and gearbox I have been building for a static workshop diorama featuring a Wespe. The castings have been 3D printed (Shapeways) then sealed using Mr Surfacer 1200 and Mr Surfacer 500.
Alastair
