1" (25.4 mm) "B" Size Ball, with Male 1/4''-20 thread
The 1/4" thread could be used to hold a camera or GPS/logger such as a Cambridge GPS-NAV (but not a Volkslogger which has an M5 thread). For that application you would also want a RAP-B-201U arm and a RAM-B-224 suction cup (for canopy mounting) or RAP-B-238U base (for instrument panel or cockpit sidewall mounting). Detailed drawing: ram-b-237.pdf