QQQ brand octal 8 pin plug with hood fits to any octal socket, black phenolic body with plated brass tube pins. Similar to '50s-'60s Amphenol pin plugs. Use this premium quality octal pin plug with snap on hood for tube testing, power supply cables etc. Made In Japan.
You will note that there is a raised 'key' on the interior surface of the hood. Some folks line this up with the QQQ in a circle logo on back of the pin plug but it all goes together fine even if you don't. It does take some moderate force to get the hood to snap onto the pin plug and lock in place. It is a bit easier if you use a very light amount of lubricant such as petroleum jelly or guitar grease on the inside of the hood.