Go to the Goodson online site www.goodson.com Look it over and you will get an idea of what the stones are and their use. Most automotive valve jobs are done with a 45 degree exhaust seat. and the valve ground at 44 1/2 degree. Intakes are usually ground to either 30 degree or 45 degree depending on the original seat. With the valve being also ground to the 1/2 degree difference to insure a good seat. Different grade stones are determined by color. Hard seats use the harder stones and some stones are general purpose.. see Goodson catalog. The pieces that fit in the guides are Pilots. They also come in many sizes. Over and undersizes in .001" increments and some are adjustable. They must fit tight in a good guide so the stone sleeve/stone assembly can cut a good seat.

A 30 degree stone will lower the final seat in the head. A 60-70 degree stone will raise the seat in the head being ground.