Chassis mount 10 pin tube / IC socket. Same mounting pattern as a TO-3 transistor. Will accept a miniature tube (no keyway!) or TO-3 case integrated circuits, such as Motorola MC1460R, MC1461R, MC1463R, MC1469R, MC1563R, and MC1569R. Very hard to find item!
3 shown for clarity, price is for one (1) socket.