If the whole point of washers is to disperse the force of screws and nuts to prevent them from digging into the material, why not simply create screws and nut heads with
Round Washer Head Screw, Type 17 Threads - in the Häfele America Shop
Type 17 Hex Head Hex Self-Drilling Screws (with washer)
Metal Self Drilling Screw Hex Head + Washer #10-16 X25 Pale Terracotta - Cl4
Buy ASSY 4 WH II steel zinc ptd. PT washer head II RW online
Kreg Screw 1 1/4″ (32mm) Fine Thread, Washer Head - M M Vic Sales and Service
Stainless Steel Philips Pan Washer Head Screw, Size: 4 x 10 mm - 4 x 50 mm
12g-14x20mm Metal Hex Washer Head Screw | Wattmaster Alco
Zinc-Plated Wood Screw, Pan Washer Head, Quadrex Drive, Coarse Thread, Regular Wood Point - Reliable Fasteners
Hobson Mungo MCS-S Concrete Screw Hex Head Washer 6mm Pack of 100 — SPF Construction Products