APC rack with threaded holes instead of cage nut inserts

Just picked up an APC 48u rack. The listing had no shots of it, and I didn’t notice till after I got it home and set up, the rack rails do not have square cage nut holes, but what appear to be threaded holes. I can not find a bolt or screw with the right size and thread pitch. It looks like it’s an M5 fine thread, but wanted to see if anyone had any info on this. Am I just supposed to get self tapping machine screws, like the previous owner did? Or is there some APC proprietary bolt that I’m working with here?