This is the P3 Glow Plug for use in the OS Max .21 VZ-V Spec and most other .18 -.28 cu in (2.9 - 4.6 cc) turbo head racing engines. FEATURES: Ultra Hot Type Plug, designed for reliable low speed and more torque at acceleration, suitable for 20% nitro fuel Ideal for novice drivers, allows easy starts and better idling INCLUDES: One P3 turbo glow plug REQUIRES: Glow plug wrench, HCAP2550 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 engines with a turbo-type cylinder head design JiM 7.20.04 ir/kh updt jxs 6/24/03 updt jxs 3/30/09