Precision Machining Black Diamond one-piece valves are made from superb quality stainless steel and machined to a profile that provide excellent flow characteristics. These lightweight valves are then impregnated by a very special process .002" deep and a surface build up, to improve wear properties and reduce friction. This process provides resistance to corrosion and wear superior to that developed by hard chromium and electro-less nickel plating. Most valves are available in either stock size with stock or thin stem and with larger head diameter for the high performance engine builder.