This kit converts the thread on Colortune and Hi Gauge Compression Tester to fit most popular sizes of spark plugs fitted to most modern and classic cars, motorcycles, garden machinery and boats.14mm to 18mm thread sizeCompression tester adaptorFor use on 14mm colortune and Hi GaugeSuitable for most modern & classic cars as well asAvailable in additional sizes 10mm,12mm,14mm or18m