US Patent 7856917 Switchblock

An adjustable gas block designed to interface with an autoloading firearms gas system. Three positions of adjustment are provided to optimize the gas flow from the barrel for the host firearm. One of the three provided positions of adjustment is selected if a silencer is in use, not in use, or if the user desires to stop the autoloading function of the firearm entirely. This design works by restricting the flow of gas from the gas port in the barrel and does not vent excess gas into the atmosphere around the gas block.