This is a Long Socket Wrench with Plug Grip from O.S. Engines.
This special glow plug wrench is for use with cowled engines or those
having deep heatsink type heads (car and helicopter engines).
It has an internal grip which holds the plug securely while it is
being withdrawn or reinserted....
A practical glow-plug wrench for universal application.
The glow-plug on being screwed into the engine is held fast by a flat spring housed inside the wrench. Thanks to the four replacement plugs being screwed into the boss of the wrench they'll always be on hand when required and keep clean....