This is the RP8 Cold Glow Plug from OS Engines for use on Most Turbo Head Racing Engines. For use with fuel containing 25% or greater nitromethane content Cold heat rating when outside temperature is high One O.S.RP8 glow plug Glow plug wrench, HCAP2550 Overall Length: 17mm (.67") Thread size: M8x.75mm This glow plug is different from the conventional glow plug. It is made to fit the inner head of engines with a turbo-type cylinder head design. lmm 6.2.11