Coil-Rite Rear Air Helper Spring Kit (4108) by Firestone Suspension. Mount inside an existing open coil spring suspension. These air springs provide adjustable spring rates far superior to the standard coil spring. The durable polyurethane air springs will support 500-1,000 lbs per set., Features: Control the air pressure in the air helper springs for varying loads and road conditions. Spring performance can be altered as easily as inflating a tire. Made of durable, elastic polyurethane. Support 500-1000 lbs. per set (not to exceed vehicles GVWR). Designed to work in temperatures between -40 F (-40 C) and 180 F (82 C). Average time of installation: 1 Hour. Manufactured in the United States. Includes: Air Helper Springs, Supports, Hardware, Air Line, Inflation Valves.