Correctly identify the thread is left-handed or right-handed, is the most basic knowledge of the valve assembly and disassembly. So, how can we find out whether the thread is left-handed or right-handed? It can be determined by the internal thread or the external thread on the valve. Under normal circumstances, they become a positive and negative thread structure, to prevent loosening of the thread. Such as the stem, the stem nut thread connection: the stem nut on the tight circle is left-handed, the handwheel thread is right-hand, stem nut trapezoidal thread left-handed. In addition, the thread angle is to the left of the thread is called left-handed; the other hand, right-handed.