On my NIDs the firing pin spacing is 15/16 inch for the .410-bore and 28-gauges, one inch for the 20-gauge, 1 1/8 inch for the 12- and 16-gauge, and 1 1/4 inch for the 10-gauge. The box body of the NID frame is the same from .410-bore to 10-gauge, just the height and width of the standing breech part changes.