Great price (compare with anyone on the internet).
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, as these seals will slide over the stock valve guides (may need to be press fit).