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Written by G.L. Huyett Marketing Department on 03/18/2020 with 0 comments

Popular Thread Series

This is a comprehensive guide to threads and their design. A thread is defined as a ridge wrapped around a cylinder or cone in the form of a helix. Threads can be tapered or straight, male or female. Please contact our engineering team at engineering@huyett.com with additional questions.

SAE STANDARD

SAE-LE threads are a common taper thread which are used primarily on grease fittings. This thread form is a modification of the standard 1/4"-28 UNF thread and is intended to thread into a parallel 1/4"-28 UNF-3B hole with a maximum minor diameter of 0.215" if a 75% minimum thread height is to be maintained. This thread type will seal heavy lubricants without the aid of thread sealant.

SAE-LT threads are often generically referred to as "taper thread."

SAE-LT Threads

AMERICAN STANDARD

American Standard Threads were adopted by the American Standards Association (ASA) in 1921. Unlike many other threads, American Standard Thread sizes are confusing by the fact that the thread designation is based off nominal pipe sizes and does not refer to any physical dimension. For example, a 1/4"-18 NPTF fitting does not have an inside or outside diameter of 1/4". This is because, during the early days of manufacturing, pipes (which were measured by inside diameter) were made much thicker than they are today, resulting in 1/4" pipes no longer measuring 1/4". External thread physical dimensions remained unchanged and retained their old 1/4" thread designations. These threads are designated with a nominal internal pipe size followed by a thread count, i.e. 1/4"-18. FULL THREADS

NPT and NPSM Threads

VARIATIONS OF THE NPTF THREAD PROFILE

PTF-SAE Short: Identical to NPTF threads, but the thread length has been reduced by eliminating one full thread from the small end of male threads or the large end on female threads. - MINUS 1 THREAD

PTF-Special Short: Identical to PTF-SAE Short threads, but with one thread removed from the large end of male threads or the small end of female threads. - MINUS 1 THREAD

PTF-Special Extra Short: Identical to PTF-SAE Short threads, but with two threads removed from the large end of male threads or the small end of female threads. - MINUS 1 THREADS

NPTF Threads

UNIFIED NATIONAL

In 1949, the American National Standard (ANS) was made obsolete and was replaced with the Unified National Standard (UNS) in an effort to increase interchangeability between American, Canadian, and British threads. Every effort was made to ensure that the threads made to the new UNS standard would mate with threads made to the obsolete ANS standard. Manufacturers were instructed to update all existing drawings to comply with the new standard. It is common to still see ANS thread types referenced. These threads are designated by a thread diameter followed by a thread count, i.e. 1/4"-28.

VARIATIONS OF THE NPTF THREAD PROFILE

UNS: Unified National Special diameter thread is an umbrella thread form which covers those thread forms which existed under the ANS standard but which do not fit into any other category.

"NS" Taper: NS Taper threads are a unique fine thread which was developed specifically for pneumatic lubricant delivery systems.

UNF, UNEF, and UNC Threads

FOREIGN STANDARD

Many thread standards exist outside the U.S. The most common are detailed below. Metric threads are denoted by an M (for standard threads) or an S (for thread forming threads) which are proceeded by a pitch diameter, followed by a thread pitch (mm), i.e. M8x1.5 or S6x1.0. Traditionally, if no thread pitch is identified, it is understood to be 1.0. British threads are denoted by a nominal internal pipe size, followed by a thread pitch (tpi), i.e. 1/4"-29.

VARIATIONS OF THE BRITISH THREAD PROFILE

BSPT: British Standard Pipe Tapered threads are a Whitworth form tapered male thread. Female threads are typically parallel.

BSF: British Standard Fine threads are a parallel threaded Whitworth form thread.

BSPP/BSPF: British Standard Pipe Parallel or British Standard Pipe Fastening threads are coarse threaded Whitworth form threads with a parallel thread profile.

German: What is often referred to as German threads are really a German designation of British coarse threads.

Variations of British Threads

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