This is the T-P8 Glow Plug for use in the OS Max .21 VZ-R and .12 TR engines.

FEATURES:

For use with fuel containing 25% or greater nitromethane content
Metal Construction

SPECS:

Overall Length: 17mm (.67")
Thread size: M8x.75mm

COMMENTS:

This glow plug is different from the conventional glow plug. It is
made to fit the Inner Head of the OS .21 VZ-R and .12 TR engines.
It has a slight taper on the bottom allowing it to sit flush
with the combustion chamber.

How to Choose the Right Glow Plug? Please refer to the following link.
http://www.osengines.com/accys/choosing-glowplugs.html