Valve guides are made from premium quality Grey Cast Iron alloy with higher phosphorous content in order to give it high wear / corrosion resistance even in poor lubricating conditions. Range: 25mm to 600mm Material: Copper Zinc Alloy, Phosphorous Bronze, Manganese Bronze,Aluminium Bronze ,Gun Metal, Alloy Cast Iron Hardness: 180 BHN to 220 BHN We also provide thread or spiral in inner diameter of valve guide to retain oil for a longer time duration.