Kit includes 12 seals

5/16 x .530 Viton Seals offer a superior seal, longer life, excellent reliability, and increased spring clearance. Viton valve seals improve the efficiency and performance of your engine by preventing engine oil from entering the combustion chamber. These seals can be used with stock or high performance single springs, single springs w/dampers, or dual springs.

No machining is required on our alloy head, as these seals will slide over the valve guides (may need to be press fit).  The valve guides on cast iron head will have to be machined, but this is an easy, fairly inexpensive operation at most machine shops.  Should be done if the head is off for other work.