CWEA Maintenance Technologist Practice Test

Which type of threads are designed to create a pressure tight and watertight seal?

1. Metric Threads

2. ACME Threads

3. BSP Threads

4. NPT Threads

The correct answer is: NPT Threads

NPT threads, or National Pipe Tapered threads, are specifically designed for creating pressure-tight and watertight seals in piping systems. The tapered design of the threads allows them to progressively tighten as they are screwed together, which compresses the two mating surfaces and forms a seal that prevents leakage of fluids or gases. This feature is particularly important in applications where the integrity of the seal is critical, such as in plumbing, gas lines, and other fluid transfer systems. The unique geometry of NPT threads, along with the use of appropriate sealing compounds or thread sealants, ensures that a reliable connection can be established. This is why NPT threads are commonly used in applications requiring stringent sealing capabilities. In contrast, while other types of threads such as Metric, ACME, and BSP have their own specific applications, they do not possess the same inherent design characteristics that specifically promote a watertight or pressure-tight seal as effectively as NPT threads do. For example, Metric threads are standardized for general mechanical applications and are not focused on sealing, while BSP threads, although they can provide seals, have different dimensions and are not tapered in the same way as NPT. ACME threads are used primarily for power transmission and do not provide the sealing