This listing is for a set of Z28 style .550" Lift valve springs. Set includes 16 springs. These springs are stock outside diameter and can be used in many 1955-1993 small block Chevy V8 cast iron cylinder heads. They work great for stock, towing and most mild performance cams and work best with cams up to 0.550" lift. Valve Spring Specifications: Spring Part Number: RV1943X Outside Diameter: 1.260" Inside Diameter: 0.785" Closed: 125 lbs. @ 1.750" Open: 325 lbs. @ 1.200" Coil Bind @: 1.160" Spring Type: Single with damper