This is the P4 Turbo Glow Plug for use in the OS Max .21VZ-B VSPEC and .21VZ-B Speed Tuned Engines. FEATURES: For use with fuel containing 25% or greater nitromethane content Also works well in most .18 - .28 cu in (2.9 - 4.6 cc) off road racing engines with turbo type racing heads YOU WILL RECEIVE: One glow plug REQUIREMENTS: Glow plug wrench, HCAP2550 SPECIFICATIONS: Overall Length: 17mm (.67") Thread size: M8x.75mm COMMENTS: This glow plug is different from the conventional glow plug. It has a slight taper on the bottom allowing it to sit flush with the combustion chamber. JiM 3.27.07 ir/jxs