These are custom hex nuts we supplied to one of our long time aerospace customers, made using 18-8 stainless steel to print with a single drilled corner on each nut.  The parts were domestically made with a lead time of 4-6 weeks for the initial release and incorporated a fine 1/4-28 thread.  In terms of the dimensions, the custom nut was very close to the standard IFI version but the added drilled hole made it uniquely fitting for the specific application.  Our internal part number is 2303-0321T and we originally supplied just 1,500 pcs of this hex nut.