The Schraer valve, invented by August Schrader, consists of a valve stem into which a valve core is threaded, and is used on virtually all automobile tires and wider rimmed (lower pressure) bicycle tires. The valve core is a poppet valve assisted by a spring. Schrader valves are also used on the fuel rail of some direct fuel injection engines and on some refrigeration and air conditioning systems, in a fitting larger than those used on tires, to allow servicing, including recharging with refrigerant. In addition, Schrader valves are sometimes used on irrigation systems to provide a place to temporarily attach a portable pressure gauge.