Hi, I am possibly a bit late to the party on this but I might be able to help for future reference. In general you are quite safe specifying the machining tolerances given in ISO 2768 MK for any non specific tolerances, save tighter tolerances for when you need a really specific fit or you will only add unneeded cost to the parts. Drilling tolerances are given by the standard drilling capabilby Hairyscreech - General