An adapter for mounting an accessory on a shroud such as is found on an M2 machine gun includes a rigid block embracing the shroud. Blunt-nosed helically threaded plugs penetrate the block and intrude partly into perforations of the shroud. Retaining rings, threaded oppositely to the threaded plugs, prevent the plugs from backing out. A key tool is provided to tighten the plugs and retaining rings. A longitudinally oriented T-rail projects radially from the block. A slide body engages the T-rail and includes a locking mechanism, a lamp assembly, a logically switched power control, a power cable, and a control cable with interchangeable switches.