Small post with spring loaded contact at the tip. Post has 2 small pins to grab when connector is inserted. Insertion is done by pushing down on connector and rotating half a turn to lock connector.
Tip # 30 Leica M3, Tip # 31 ASA Bayonette, Tip # 32 Wein Phillips, Tip # 34 HH w/ Round CTR Pin, Tip # 35 HH w/ Third Blade, Tip # 36 1/4 (Monolite) Molded Straight, Tip # 37 3.5mm Plug Molded Straight, Tip # 38 2.5mm Microsync, Tip # 39 2.5mm Molded Straight, Tip # 40 Graflex Solenoid