Schedule 10 vs Schedule 40

The schedule number on pipe products relates to the thickness of the wall on the pipe: as the number increases, the thicker the wall thickness becomes. Also, while the schedule number can be the same on different sized pipes, the actual wall thickness will be different. 

  Wall Thickness
SizeODSch 10Sch 40

ANSI B1.20.1 – NPT – American National Standard Taper Pipe Threads

NPT and NPTF pipe threads – dimensions according ANSI/ASME B1.20.1/3.

For NPT threads a sealant compound or Polytetrafluoroethylene (PTFE) tape must be used for a leak-free seal. For NPTF no sealant is needed for a leak tight connection. NPTF threads are the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.

NPT threads may be referred to as MPT (‘Male Pipe Thread’), MNPT, or NPT(M) for male (external) threads, and FPT (‘Female Pipe Thread’), FNPT, or NPT(F) for female (internal) threads. Note that FPT and MPT are not authorized designations per the ANSI standard.

Characteristics of NPT (also known as ANSI/ASME B1.20.1 Pipe Threads, General Purpose):

Note! Pipe sizes do not refer to any physical dimensions. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. A 3/4″ NPT pipe thread has an outside diameter – OD – of 1.050 inches. Each thread size has a defined number of threads per inch – TPI, or pitch. The 3/4″ NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because more than one size have the same TPI.

ANSI B1.20.1 – NPT – American National Standard Taper Pipe Threads1)
Pipe Size
TPIApproximate Length of Thread (inches)Approximate Number of Threads to be CutApproximate Total thread Makeup, Hand and Wrench (inches)Nominal Outside Diameter Pipe
Tap Drill

2-1/2″81 1/2127/82.8752-5/8
3″81 1/21213.5003-1/4
3-1/2″81 5/8131 1/164.0003-3/4
4″81 5/8131 1/164.5004-1/4
4 1/2″8

5″81 3/4141 3/165.5635-9/32
6″81 3/4141 3/166.6256-11/32
8″81 7/8151 5/168.625 
10″82161 1/210.750 
12″82 1/8171 5/812.750 



1) The taper rate is 1 in 16 inch (3/4 inch in a foot or 62.5 mm in a meter)

NPT threads are not interchangeable with NPS – National Pipe Straight – threads.

Example – Typical Designation of NPT thread:

NPT threads may look similar to ISO 7-1 threads. However, ISO and NPT threads should not be mixed. ISO threads have 55o taper angle versus 60o for NPT. The NPT root and crest configurations are also different from ISO. For ISO threads pitch is usually measured in millimeters (may be expressed in Inch). The pitch is different.

Note that both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and flat peaks and valleys.

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Related Topics

Sizes and dimensions of pipes and tubes, and their fittings – inside and outside diameter, weight and more.

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Pipe threads where pressure tight joints are made on the threads – Part 1: Taper external threads and parallel internal threads.

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NPT – Briggs Standard Pipe threads – Taps and Drill Sizes.

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BSPP (G) – British Standard Pipe Parallel and BSPT (R/Rp) – British Standard Tapered Pipe for pipes and tapered threads – G/R/Rp.

Taps and drill sizes used for Whitworth – ISO 7 and ISO 228 threads.

The content in The Engineering ToolBox is copyrighted but can be used with NO WARRANTY or LIABILITY. Important information should always be double checked with alternative sources. All applicable national and local regulations and practices concerning this aspects must be strictly followed and adhered to.

The Engineering ToolBox (2004). ANSI B1.20.1 – NPT – American National Standard Taper Pipe Threads. [online] Available at: [Accessed 19/9/2023].