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[Useful] Basic Pipe Thread Ordering Guide

Posted by Troy Stiffler on 11th Dec 2014

Back to Earth Surplus stocks many refurbished Ridgid pipe fabrication tools.

About Ridgid

Since 1923, RIDGID has remained the symbol of certainty to dedicated professionals of the expert trades. Every tool that bears the RIDGID brand is engineered to the same high standards of quality, strength, and endurance, as was that first heavy-duty pipe wrench more than 80 years ago. Ridgid covers its products with a lifetime warranty against defects in material or workmanship for the life of the tool.

Choosing The Right Thread Type

NPT – This is the most common standard in the USA. If you’re not sure what thread you require, it’s likely the NPT. National Pipe Thread Taper (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings. In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal. In America, William Sellers set the standard for nuts, bolts, and screws which became the National Pipe Tapered Thread (NPT) in 1864. Commonly used sizes are 1⁄8, 1⁄4, 3⁄8, 1⁄2, 3⁄4, 1, 1 1⁄4, 1 1⁄2, and 2 inch, appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than 1⁄8 inch are occasionally used for compressed air, while sizes larger than 2 inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes. NPTF indicates a “female” thread. NPTM indicates a “male” thread.

NPSM - The National Standard Free-Fitting Straight Mechanical Pipe Thread (NPSM) piping convention refers to pipe thread that is not tapered. NPSM pipe threads do not seal as effectively as NPT threads.

BSPT and BSPM - The British Standard Pipe (BSP) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread and has been adopted as a standard scale used in plumbing fittings, except in the United States where NPT is the standard used. Two types of threads are distinguished: Parallel ('straight') threads, British Standard Pipe Parallel thread (BSPP; originally also known as[1] British Standard Pipe Fitting thread/BSPF and British Standard Pipe Mechanical thread/BSPM), which have a constant diameter; denoted by the letter G. Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R. A list of 16 thread sizes are defined by the standards, ranging from 1⁄16 to 6. The size number was originally based on the inner diameter (measured in inches) of a steel tube for which the thread was intended, but contemporary pipes tend to use thinner walls to save material, and thus have an inner diameter larger than this nominal size. In the modern standard metric version, it is simply a size number, where listed diameter size is the major outer diameter of the external thread. For a taper thread, it is the diameter at the "gauge length" from the small end of the thread. The taper is 1 to 16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.

UNC (Coarse) and UNF (Fine) (Bolts Only) - The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It has the same 60° profile as the ISO metric screw thread, but the characteristic dimensions of each UTS thread (outer diameter and pitch) were chosen as an inch fraction rather than a millimeter value. The UTS is currently controlled by ASME/ANSI in the United States. The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch. For diameters smaller than 1⁄4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given. This number pair is optionally followed by the letters UNC, UNF or UNEF if the diameter-pitch combination is from the “coarse”, “fine” or “extra fine” series, and may also be followed by a tolerance class.

Choosing The Right Die Type

Alloy RH - For right hand threading. This is the basic standard for “manual” pipe threading.

High Speed RH - For right hand threading. High speed dies are required if using your die head in conjunction with a machine threader. They are made of stronger materials which allow for faster threading.

High Speed LH - For left hand threading. High speed dies are required if using your die head in conjunction with a machine threader. They are made of stronger materials which allow for faster threading. LH threading is not a common method.

Alloy for JIS RH – Japanese International Standard for right hand threading.

British ISO Alloy RH – British standard for right hand threading. Available in metric sizes.

Note

Ridgid provides thorough solutions for pipe threading. Some die types are not available in all sizes. If you have a selected your required thread/die type, and do not see the size you require, it is because Ridgid does not manufacturer the die/thread/size combination requested.