I have been known to use 8mm (7.75mm) coach bolts with the end squared off to 14.75mm and you have to grind a bit of the dome away so as to slide up the slot. I made some in 6mm too.
Forgot to say I have a hold down kit as well but they only supply 4 tee nuts and it depends on how wide to top of the slot is mainly since the studding in the kit is 10mm which is big when it comes to small milling tools.
They work for me
Edited By Jesse Hancock 1 on 16/04/2015 17:01:54