For quick removal/installation of valve collets, firmly push or tap tool with a hammer, magnet in tool captures collets. Can be used with cylinder head in situ or on work bench. Ideal for replacing broken valve springs or valve stem oil seals without removing the head from the engine. For in situ use, a suitable adaptor (not included) will be required to allow compressed air into the combustion chamber to hold the valve closed while compressing the valve spring.