V-Thunder valve spring kits are made from the finest materials available and manufactured to close tolerances. The complete spring kits contain springs, retainers, valve keepers and spring seats and fit 1984-1999 Big Twins and 1999 to present Twin Cam models. Spring kits are interference wound double springs with a damper. The damper keeps the inner and outer spring coils from locking together and helps to control harmonics in the valve spring. Valve keys, seats and retainers are made from the high grade chrome-moly steel. Retainers are also available in titanium. These kits are designed for use with High Performance or Racing engines. Spring seat measurements are; thickness .080", inside diameter .585" and outside diameter 1.500". All parts heat treated to the highest industry specifications to cope with the excessive demands of powerful V-Twin engines. All parts in these spring kits are separately available. Valve keys are available for Sportster models 1957 to present and Big Twin 1948 to present.