Valves are yellow, lead brass, copper valves and aluminum alloys. The machinability of lead brass is directly proportional to the lead content, but when the lead content exceeds 3%, the machinability of brass will not be improved obviously, and the strength, hardness and elongation of brass will decrease. Therefore, the maximum lead content of cutting brass is about 3%. The technological properties and uses of lead brass commonly used in China are: (1)HPb63-3. Also known as free-cutting brass, it has high strength, good cold working performance and excellent cutting performance. Many countries set its machinability as 100% as the relative standard of copper alloy machinability. HPb63-3 is mainly used to manufacture high-precision parts of clocks and other mechanical instruments, such as movement, gear, small shaft and bearing. HPb63-3 is α single-phase brass, which has poor hot workability and can only be hot extruded in hot state, resulting in low efficiency in producing strip. Since 1980s, it has been gradually replaced by HPb60-2. (2)HPb60-2. Although the cutting performance is slightly inferior to HPb63-3, it can be processed in hot state, with uniform distribution of lead particles, good milling performance, no warping after long-term use, good stability, high hardness and strength after stress relief, and its comprehensive performance is superior to HPb63-3. It is mainly processed into plates and strips by pressure, which are used to manufacture movement parts and high-precision parts of watches and clocks and mechanical instruments.