A printed adapter now stands in for the factory rear sight on selected Thompson guns so a red-dot optic can sit on top. The same piece still works as an iron rear sight when no optic is fitted, thanks to a center groove.

It attaches to the M1927 A1, the 1928, and any other Thompson whose rear sight uses four screws.

Builders are told to print it with eleven walls at full infill in PA-CF6 or PLA+. Four 8-32 machine screws no longer than 10 mm secure it, and those screws must be cut short enough that the bolt can still travel freely.