These are made from Apco-45, because of its ideal characteristics for the application, such as resistance to wear because of a 4-5% nickel content, greater heat conductivity because of the approx 80% copper content.
You will need to measure your stock valve guide hole to determine the size to order. Each and every head will be different depending on wear and how much material is removed when the old guides are pressed out.
*Note - Valve Guides are sold each. You must order 4 for a complete set.