Sealey vs518 spark plug feeler gauge metric sealey vs518 p this spark plug feeler gauge from sealey is specially designed for gapping spark plugs and suitable for both traditional copper and precious metal plugs features an electrode adjuster allowing the electrode to be adjusted without levering against the core which can be easily damaged blade sizes 0 5 0 6 0 7 0 8 0 9 1 1 1mm p sealey vs518 spark plug feeler gauge metric