On the Flues 28-gauge guns I've had experience with the rib extension bolting is different then on the larger bore Flues guns. My 1915-vintage No. 1 Special 28-gauge --

The rib extension used on larger bore Flues Models --

As to the NID frames, the actual box part of the frame is within a file stroke or two of the same on all NIDs from the Super-Ten down to the .410-bore. The height and width of the standing breech and the firing pin spacing changes. The height and width of the standing breech and the firing pin spacing is the same on the .410-bores and the 28-gauges. Also there is the taller standing breech frame in each gauge for the vent rib guns. A Super-Ten and a 28-gauge, both No. 2s --
