Octal base valve (tube) socket pcb mount. Can be ceramic or other (Bakelite, plastics etc.).
The orientation is such that the components would go on one side of the board (the facing side)
and the socket on the other side (thus mounted it would protrude thru chassis). You observe the
pins of the socket from the "back" side therefore, pin 1 is in 6:30 position progressing CW till
pin 8 is in the 5:00 oclock position, with the gap being between, 1 and 8.
This gap is usually used to index the valve position for:
> thermal/cooling design considerations (at least 1.5X of envolope dia. space between valves 2X would give saftey margin).