I installed 18 platenuts on the bulkhead flange. First I drill thru all the rivet holes with a #40 bit and debur the bottom and countersink the top. I run my #40 countersink bit in the rivet holes to make a small countersink. I do this operation now with an electric drill so that the countersink bit stays straight in the hole. I'm using the NAS rivets which have a small head and don't require a large countersink in order to fit flush.
Then I enlarge the center hole to fit the 8 size screw. I use a #20 drill for this. #21 is the 3/16 inch size, but it is just to tight on the threads and rubs to much. One size larger is just a clean clearance. I debur top and bottom of the large hole.
Then I mount the plate nut using a cut off screw through the center hole and pull the platenut up in place. I install both rivets and squeeze them.
This process makes for a pretty fast process and gets the holes deburred.
