How do you determine NPT fitting size?

As a general “rule of thumb” an NPT thread is approximately 1/4″ (0.25”) larger than its “name.” For a 1/4″ NPT fitting the “nominal” OD is 0.533”. NPT fittings are slightly tapered so the “nominal” diameter is the diameter in the middle of the threaded portion, as measured by the top (crest) of the threads.

What are the NPT sizes?

Commonly used sizes are 1⁄8, 1⁄4, 3⁄8, 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 4, 5, and 6 inch, as pipe and fittings by most U.S. suppliers. Sizes smaller than 1⁄8 inch are occasionally used for compressed air, while sizes larger than 6 inches are often joined by other methods.

Is NPT measured by ID or OD?

How are they measured? NPT fittings are listed by the “standard” inner diameter (I.D.) of the fitting. (We put “standard” in quotes because the I.D. of the fitting will vary, depending on the manufacturer.) The outer diameter (O.D.) of the threads is usually about 1/4 (0.250) in.

How are outside threads measured?

When measuring a female pipe thread (FPT), measure the OD of the pipe itself and subtract ¼ inch to find the correct pipe thread size. Perhaps even easier than this is to purchase a measuring tool called a caliper that will measure OD and inside diameter (ID).

What size NPT is garden hose?

Threads are garden hose thread (GHT), which is 3/4″ diameter strait (non-tapered) thread with a pitch of 11.5 threads per inch (TPI) on one end and tapered NPT (National Pipe Thread) on the other.

Will NPTF fit NPT?

NPTF threads will screw together with NPT threads and should have no noticeable assembly problem. There will most likely be an interference fit between the root and crest on either the major or minor diameter of the thread, depending on which part is NPTF. To accomplish a seal on the joint, a sealant will be required.

How is NPT measured?

NPT is defined by ANSI/ASME standard B1.20.1. The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length (3⁄4 inch per foot or 62.5 millimeters per meter) measured by the change of diameter (of the pipe thread) over distance of thread.

What is the nominal pipe size?

Nominal pipe sizes generally range from 1/8 inch all the way up to 12 inches. Increments go up 1/4 inch between these two figures. The outside diameter of the pipe does not necessarily increase at a rate that is proportional to the rate of increase in the nominal size.

How do you measure pipe thread size?

You can determine the size of pipe threads ( NPT /NPTF, BSPT , BSPP) by measuring the outer diameter and comparing it with the profile, or in other words, by subtracting ¼ inch. For non-pipe threads (UN/ UNF , Metric Parallel, Metric Tapered), determine the size by measuring the outer diameter using a caliper.