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. 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.