Coil spring is a helical spring that offers resistance to a compressive force applied axially. Most coil springs with material diameter less than 9mm are cold coiled. Almost all custom coil springs using over 14in bar stock are hot coiled. There is an overlapping area from 9mm to 14mm material size in which the custom coil springs may be either cold coiled or hot coiled. The transportation industry is the largest user of hot coil springs. Buy from globe to your place.