Threads are a key element in mechanical engineering and hydraulics. The most popular standard in Europe is the BSP thread (i.e., G), in the US rather NPT thread - but one of the popular standards used in some specific industries is the SAE thread. In this article, we will take a closer look at this standard, its applications, and the differences compared to other thread systems.
SAE (Society of Automotive Engineers) is an organization dealing with standards for the automotive and mechanical industries - and it introduced the SAE thread standard. SAE threads, also known as UN (Unified Thread) threads, are widely used in hydraulics, pneumatics, and mechanical constructions. What interests us the most - they are often used in applications with gaseous media because they are considered to provide the most reliable guarantee of tightness. They are used, for example, in systems with refrigerants, heat pumps, air conditioning systems, etc.
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SAE threads are divided into several categories - let's say types, of which the most important are:
SAE threads are widely used in various industries, including:
Although metric threads are dominant in Europe, SAE threads are still more commonly used in the United States and Canada. However, they can also be found in the industries mentioned above. Here are the key differences:
The SAE thread standard (UN) was introduced after World War II - in 1949 as a unified thread system for the USA, Canada, and the United Kingdom. It was created as a result of collaboration between the Society of Automotive Engineers (SAE), the American Standards Association (ASA, now ANSI), and the British Standards Institution (BSI). It was and remains, as you can see, mainly a domain of Anglo-Saxon countries. It spread worldwide with globalization processes.
The goal of introducing the SAE thread - in post-war times - was to unify standards and simplify the production and maintenance of machines, as different thread systems were used before, e.g., Whitworth thread (BSW) in the UK and American threads (USS and SAE) in the USA. These countries already during World War II (when their technological cooperation tightened due to being in the same political camp) - recognized discrepancies in thread standards as a serious obstacle to the development of cooperation, trade, etc.
You can find the SAE thread dimensions below.
|
Thread size |
Nominal |
Thread pitch |
External thread |
Core diameter |
|
1/4"-20 UNC |
6,35 |
1,27 |
6,223 |
4,699 |
|
1/4"-28 UNF |
6,35 |
0,91 |
6,35 |
5,059 |
|
5/16"-18 UNC |
7,94 |
1,41 |
7,899 |
6,299 |
|
5/16"-24 UNF |
7,94 |
1,06 |
7,975 |
6,703 |
|
3/8"-16 UNC |
9,53 |
1,59 |
9,525 |
7,85 |
|
3/8"-24 UNF |
9,53 |
1,06 |
9,538 |
8,404 |
|
1/2"-13 UNC |
12,7 |
1,95 |
12,7 |
10,863 |
|
1/2"-20 UNF |
12,7 |
1,27 |
12,7 |
11,373 |
|
5/8"-11 UNC |
15,88 |
2,31 |
15,875 |
13,889 |
|
5/8"-18 UNF |
15,88 |
1,41 |
15,875 |
14,536 |
|
3/4"-10 UNC |
19,05 |
2,54 |
19,05 |
16,977 |
|
3/4"-16 UNF |
19,05 |
1,59 |
19,05 |
17,703 |
The table contains SAE thread dimensions – divided into external and internal threads and categorized into UNC and UFC.
SAE threads are an essential component in the mechanical, hydraulic, and automotive industries. Their standardization allows for use in a wide range of applications, although their popularity is limited geographically and by industry. Understanding the differences between SAE and metric threads is crucial when working with mechanical and hydraulic systems.
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