These 635 series heavy duty custom pneumatic retracts are designed for specific R/C aircraft weighing up to 32 lbs.. These retracts are constructed the same as the standard 630 series retracts with heat treated aluminum alloy frames and trunions, these gear will accommodate a 1/2" diameter RoboStrut or a custom made 5/8" dia. 4130 chrome moly steel tubular RoboStruts. They offer long dependable service for large aircraft flying off grass or paved runways. Powered by a 5/8" bore triple sealed Robart air cylinder, all of these units feature positive up and down locks.