Thread standards, you need to know
You always have to deal with thread standards when you want to cut a thread yourself or are looking for suitable components for a project. If you use the wrong thread standard, the screw will not fit and you will have to start all over again. Maybe you don't notice the mistake at first, but later you have to deal with jammed threads or increased wear.
To prevent this from happening to you, we have compiled a clear overview of everything you need to know about thread standards. At BAER, we live and love threads - and of course we know all about the common thread standards. We explain what a thread standard actually means and which thread standards you should definitely know.
Thread profiles are determined by thread standards
Thread standards are essentially a number of parameters that precisely describe the profile of a thread. In this way, a specific thread can be reproduced as desired. In this way, the thread standard ensures that threads become interchangeable and always retain their individual thread profile, even across temporal and spatial boundaries.
The most important parameters for thread standards
The parameters specified in the thread standard may differ slightly in individual cases. In any case, the diameters are important. Three different diameters can be distinguished for a thread: the outer diameter or nominal diameter is the largest of the three, the core diameter the smallest. And the pitch diameter is halfway in between.
And two other parameters are essential for thread standards. The flank angle is the angle between two adjacent thread flanks. Finally, the pitch plays a role. Its value differs for metric and imperial standards. For metric thread standards, it is the distance between two thread tips, for inch threads, the number of threads per inch is used to calculate the pitch.
Thread standards - Thread abbreviations
Each thread standard can be easily identified by its thread abbreviation. This consists of a code letter followed by the nominal diameter or - depending on the thread standard - the thread size. The abbreviated designation can also contain other information, such as the number of threads, the tolerance, and a reference to multiple threads.
Standard thread as the most common thread standard in Europe: The ISO metric thread
The ISO metric thread is the standard for threads in Europe. So you've almost certainly had to deal with this thread standard at some point. If you use commercially available screws, nuts or threaded rods, then this is the ISO metric thread.
The standard for the metric ISO thread specifies a flank angle of 60°. The thread designation is composed of the letter M and the nominal diameter. For all metric threads, the pitch also corresponds to the distance covered in one revolution.
In addition to the metric standard thread, there is also the metric fine thread MF, which also has a flank angle of 60°. According to this standard, the metric fine pitch thread has a smaller pitch and a smaller thread depth than the standard thread.
International thread standards under the microscope
Outside Europe, other thread standards are much more widespread than the ISO metric thread. These international thread standards are mostly inch threads, which you need to be aware of, especially when it comes to thread designations. Two thread standards in particular have become globally accepted:
American thread standards
A whole series of thread standards with different characteristics are grouped together under the designation Unified Thread Standard (UTS). Common to all of them is the flank angle of 60°. It is important to note that with the American thread standards you must count the number of threads per inch to determine the pitch.
American thread standards include the Unified National Coarse Thread (UNC) as the American coarse thread and the Unified National Fine Thread (UNF) as the American fine thread. In their function and application, they correspond approximately to the metric thread standards. In addition, there are various special threads and pipe threads. The American thread standards have spread far beyond the borders of the USA and are also used to some extent in Asia, South America and Australia.
British thread standards
The British thread standards also bear the title Whitworth thread. The designation goes back to the father of standards for threads, the British engineer Joseph Whitworth. The catchment area of the British thread standards is - unlike the American standards for threads – mainly limited to the country of origin. But that doesn't mean you won't come across one in this country. Especially in the plumbing sector, the Whitworth pipe thread has established itself as the standard for threads.
The British standards are also measured in inches, but the flank angle here is only 55°. The British Standard Whitworth Coarse (BSW) as the British coarse thread and the British Standard Fine (BSF) as the British fine thread can be roughly equated to the metric equivalents.
Thread standards for special applications
In addition to these international variants of the thread standards, there are then standards for threads with special profiles or areas of application. These include the Trapezoidal thread (Tr), the saw thread (S) and the cylindrical round thread (Rd). Due to their special geometry, all these thread standards are particularly suitable for use as movement threads. Trapezoidal threads can be found, for example, on the lead screws of lathes, while round threads are used in rough working environments such as on railroad cars thanks to their high resistance to contamination.
In addition, there are numerous other thread standards with even more specific applications. Standards for lens threads of cameras or thread standards for bicycle threads are just two of many examples.
Thread standards in BAER Online-Shop
In your everyday life as a craftsman or do-it-yourselfer, you will get by with the metric ISO thread in most cases. In our BAER Online-Shop you will find a large selection of taps and other tools for this thread standard. But also for every other case you are well equipped with BAER as a tap manufacturer. We have American and British thread standards in our program in large quantities. Also special standards like the trapezoidal thread, the round thread, the saw thread or the valve thread are no problem for us. And pipe threads can also be cut with BAER tools according to various thread standards. Take a look at our product portfolio and see for yourself! If you have any questions, requests or suggestions, please do not hesitate to contact our customer service.