NOTE the item is red Easily adjust the gap with this spark plug tool Fits the following spark plugs : 10/12/14/16mm (DOES NOT fit 18mm spark plugs) Which gap is best? The exact spark plug gap (electrode gap) depends on the engine design, the strength of the ignition system and how much power the engine produces. Original engines : Usually 0.71.1 mm depending on the engine model and manufacturer's specification. Trimmed engines / turbo engines : Often smaller gaps, e.g. 0.60.7 mm, to reduce the risk of spark blowout under high boost pressure. E85 or methanol fuel : The ignition system often has to work harder - sometimes even tighter gaps are needed, e.g. 0.50.6 mm, if the spark has difficulty igniting the mixture. Advantages of tighter spark plug gaps Less risk of spark blowout under high boost pressure In engines with high cylinder pressure (e.g. turbo or supercharger), a large gap can cause the spark to "blow out". A smaller gap is more stable under these conditions. Lower voltage