Ref - L-OS71641500 -
The plug for all O.S. multi-cylinder and 4~stroke engines. Long reach, long life
This plug is also useful where you want to an engine rich and still have a good tick over.
Glow plugs are considered to be consumables - But by using a low voltage to start ( under 1.5 volts) and not burning the plug dry, you prolong the life of your glow plug. It is also worth washing out a new engine after running in to prevent small particles shorting the plug and destroying it. Blowing plugs on new engines is less common now a days, but is still something that can happen.