Since sealing compounds will be used for NPT threads, only a single plug with a step, known as an L1 plug (internal thread) or a single thin L1 ring (external) are required to check size.

• 因为NPT螺纹要使用密封剂，只要用一个塞规，大家叫L1规（内螺纹）或L1环规（外螺纹）来检查尺寸。