Thats why I selling the taller Acorn nuts, and my washers are 0.040" thick, how much are your stud threads hanging out?
Washers are .040" thick x 16mm OD x 8.4mm ID #110 Alloy Half Hard
Acorn Nuts are Plated & Flanged, 16.75mm Flanged Base -Smooth Bottom X 16.50mm tall, Head Size is 12mm (Wrench Size) 15.90mm deep.