Great price (compare with anyone on the internet).
Kit includes 12 seals

5/16 x .500  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. 

Machining may be required, however we recommend these seals for two reasons. First, the smaller diameter of the seal increases the valve spring clearance (distance between the outer surface of the seal and the inner surface of the valve spring). This may be required when using a single spring with a damper, or with dual springs. Secondly, machining the valve guide (which is done with a valve guide cutter), and press fitting the seal, prevents the seal from sliding upwards even after the seal drys out and/or hardens over it's service life. Note the small groove which is machined into the guide during the process, which helps to ensure that the seal will stay put, long after other seals have failed.

For those who desire the benefits of a Viton Seal but are unable to machine the guides, we also offer a .530 seal which slides over the valve guide without machining.