having my plates sent of to be milled and drilled so i really dont want to make any mistakes here. so if i go of the bk12 ballscrew support here then the hole diameter according to the spec sheet is 6.6mm so then when adding tapped holes in cad (solidworks) and i select m8 tapped hole it gives me 6.8mm not 6.6mm is this correct or should i manually change the m8 from 6.8 to 6.6mm?

hope im making sense here