Wraith,
Nothin' gets under a tool, diemakers or assembliers skin then someone who cuts a c'bore to a screw diameters depth. Besides the tolerance of cap heigth, wear on the pilot-c'bore step drill outside radius, sprung lock washers or plain washers, and chips in the hole, when they assemble, the head always sticks up over the steel needing a dis-assembly to recut the hole depth. In the old days you set your depth from the thread depth and the thickness under the c'bore using a stock screw "under the head length" ensuring at least a sixteenth clearance between the shcs and the top of plate to allow for stuff on the screw.
Just wandering
rentapen