Insure against valve spring fatigue and breakage and stop that valve float with the best valve springs on the market! Hand checked and magnafluxed for top quality. The Outer spring is 1.246" diameter using .153" wire diameter and the Inner features .910" diameter using .113" wire diameter. Together they will lift .630" and more with coil bind at .800". Valve guide boss must be machined for all dual spring kits.