Cast 319 aluminum blast gates are available in both half and whole versions, 2″ to 22″. Blast gates are used to either control a branch of a system, a run to a specific machine or for balancing. The collar of the whole gates are tapered to allow for a tolerance on the exact diameter of the duct. Half gates are usually used in a retrofit of a system where a 180 degree section is cut out of the duct and the collar is intended to straddle the duct.