What is the amount of taper on a National Pipe Taper (NPT) thread?

The amount of taper on a National Pipe Taper (NPT) thread is standardized at 1 inch of taper over a length of 12 inches, which translates to 1/4 inch per foot. This means that for every foot of length of the threaded section, the diameter decreases by 1/4 inch.

Tapered threads like NPT are designed to create a tight seal when interconnected, as the taper helps to ensure that the threads draw together under pressure, compressing the material and minimizing the risk of leakage. In practical applications, this specific taper is crucial for ensuring compatibility and helping to create leak-proof joints in piping systems. The use of 1/4 inch per foot taper ensures a gradual decrease in size, allowing for proper engagement and sealing capability without excessive force that could damage the threads.