What is this 1950's tubless logic plugin?

I purchased it ebay along with the pictured 1950's vintage Vacuum Tube Logic plugin, in May 2005 for about $100.00

I can only guess as to the usefullness of the tubeless plugin. It is a tube extender because ther is no tube socket on top.

Please contact me if you have any clue.

1950's Tubeless plugin
1950's Tubeless plugin

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