How to measure NH, NST, and NPT threading

Measuring NH (National Hose) and NST (National Standard) Threadings

NH threads are commonly used in firefighting equipment due to their reliability and durability. Here’s how to measure NH threadings effectively:

• Thread Pitch: Use a thread pitch gauge or ruler to measure the distance between the crests (high points) of adjacent threads. NH threads typically have a standard pitch depending on their nominal size.
• Thread Diameter: Measure the outside diameter (OD) of the male thread and the inside diameter (ID) of the female thread using calipers or a measuring tape. This helps determine the nominal size of the thread.

Measuring NPT (National Pipe Thread) Threadings

NPT threads are tapered and widely used in plumbing and piping applications to create a seal against leaks. Here’s how to measure NPT threadings accurately:

• Thread Taper: NPT threads have a taper of 1 in 16 on the diameter. Measure this taper using precision tools to ensure a proper fit with fittings.
• Thread Pitch: Measure the threads per inch (TPI) by counting the number of threads along the length of the threaded portion.
• Thread Diameter: Determine the nominal size by measuring the OD of the male thread and the ID of the female thread. This measurement is crucial for selecting compatible fittings.

NH and NST

Nominal Size (inches) | OD (inches) | TPI (Threads per Inch) 

----------------------|-------------|----------------------- 

1/2 | 0.75 | 8

1 | 1.00 | 11.5

1 1/2 | 1.25 | 9

2 | 1.50 | 8

2 1/2 | 1.875 | 7.5

3 | 2.125 | 7

3 1/2 | 2.375 | 6

4 | 2.625 | 6

4 1/2 | 2.875 | 6

5 | 3.125 | 6

5 1/2 | 3.375 | 6

6 | 3.625 | 6

NPT

Nominal Size (inches) | OD (inches) | TPI (Threads per Inch) 

----------------------|-------------|----------------------- 

1/8 | 0.405 | 27

1/4 | 0.540 | 18

3/8 | 0.675 | 18

1/2 | 0.840 | 14

3/4 | 1.050 | 14

1 | 1.315 | 11.5

1 1/4 | 1.660 | 11.5

1 1/2 | 1.900 | 11.5

2 | 2.375 | 11.5

2 1/2 | 2.875 | 8

3 | 3.500 | 8

3 1/2 | 4.000 | 8

4 | 4.500 | 8

5 | 5.563 | 8

6 | 6.625 | 8

Example Measurements for NH and NPT Threads

Here are some example measurements for common sizes of NH and NPT threads:

NH (National Hose) Thread Example:

• Nominal Size: 2 inches
• Thread Pitch: 8 threads per inch (TPI)
• Thread Diameter:
  • Male Thread OD: 1.50 inches
  • Female Thread ID: 1.875 inches

NPT (National Pipe Thread) Thread Example:

• Nominal Size: 1/2 inch
• Thread Taper: 1 in 16
• Thread Pitch: 14 threads per inch (TPI)
• Thread Diameter:
  • Male Thread OD: 0.840 inches
  • Female Thread ID: 0.710 inches