The black "Start" button KU-11M, used in the former USSR to starting the machine-tools, electrical machines and mechanisms. The ring around the button shows its parameters and the year of manufacture - 1972 (there is one 1971). It designed to operate at a current of 6A, alternating voltage up to 380V or constant voltage up to 220V. When the button is pressed, two of the four contacts work for closing and possibly two other contacts for opening. Size 1.6x1.6x2.1" / 40x40x53 mm Button diameter 0.94" / 24 mm