Here's one:
http://www.r-type.org/exhib/abc0004.htm
The socket has a thin metal skirt which surrounds and guides the larger diameter section of the envelope just above the pins.
Not too visible in the photos, there is a pip moulded into the glass on the lower left side. The shirt on the socket has a shaped slot to spring out and allow the pip past. The bottom of the slot ends in a circular hole to accept and retain the pip.
These valves could be devils to unplug after years and were too easily broken. Sometimes the skirt cracked the pip off and let air in.
As a kid, I hated the things. Any I acquired went straight in the bin.
I also didn't bother with Mazda Octal. This was a distorted version of International Octal. Deliberately incompatible to force set users to only buy one brand of replacement valves. Evil!
David