Description Fitment Forged one-piece construction to help with weight reduction & improved flowPerformance valves receive a swirl polish, smooth stem treatment, and are made of 21-2n/suh35ht stainless steelSprings are made of swosc-v material (oil-tempered steel wire)Some springs feature a progressive style design with more coils on one end of the springProgressive springs are heavier on one end and should always be installed towards the bottomNon-progressive springs are paint marked and should be installed towards the top