Park Tool VC-1 Valve Core Tool

Park's Valve Core Tool is great for tightening, removing and installing Schrader and Presta valve cores (the cores are inside the valve), and also Presta valve extenders that have 5mm wrench flats. It's a Handy tool to save a tube when all that's wrong is a broken valve, and it also lets you remove valves to easily insert sealant.