Very interesting - threaded inserts cut to accept machine screws . . . is Russ a cabinetmaker too?

No, but he has used the same techique on duck guns for the installation of both thick and thin pads so depending on clothing one or the other can be used. Not as easy as pads of 3 different thicknesses that pop in and out of a Benelli SBE II hollow plastic stock but useful none the less.