Thread standards – Everything you need to know

DIN and ISO - you can't get around these two abbreviations when looking for the right tool these days. Behind them are the German Institute for Standardization (DIN) and its parent organization, the International Organization for Standardization (ISO). What sounds very bureaucratic at first is actually an important tool for every craftsman and hobbyist. Because even if you feel overwhelmed by the multitude of different thread standards at first - it is only thanks to them that you can find all the utensils you need at first glance. And the topic of thread standards is not as complicated as it first seems. We at BAER Tools will give you a brief overview. Please click on the thread standard and you will learn more about it.


M = ISO metric thread

UNC = American Unified Coarse Thread according to ANSI B1.1

UNF = American Unified Fine Thread according to ANSI B1.1

BSW = British Standard Whithworth Coarse Thread BS 84

BSF = British Standard Whitworth Fine Thread BS 84

G (BSP) = British Whitworth pipe thread DIN ISO 228

BA = British Association Standard Thread BS 93

BSB = British Standard Brass Thread

BSC = British bicycle thread RS 811

NPT = American taper pipe thread ANSI B 1.20.1

8-UN = 8-UN thread ANSI B1.1

Which dimensions are defined by thread standards?

Each thread has its own thread profile that distinguishes it from other types of threads. The thread profile results from the cross-section of the external and internal thread and shows all relevant dimensions that make the thread distinctive. These dimensions are defined by the thread standard.

What are these dimensions? First of all, each thread profile has three significant diameters. The most important is the outside diameter, which is also called the nominal diameter because it is usually used as the thread designation along with the abbreviation of the thread standard. Next is the flank diameter, which is needed to calculate the flank angle, among other things. The smallest diameter in the thread profile is called the core diameter. And two other values play a role for the thread standard: The flank angle designates the angle between two adjacent thread flanks. The pitch designates the distance between the two flanks of a thread or from thread tip to thread tip. All values are specified metrically or in inches, depending on the thread standard.

Thread standards standard in Europe: The ISO metric thread

In your own work, you will predominantly encounter the metric standard thread, because this is the one most commonly used in Europe for screws, nuts and threaded rods. It is characterized by a 60° flank angle and by the specification of its dimensions in metric units of meters instead of inches.

The DIN 13 standard distinguishes between regular threads and fine threads with a narrower thread profile. Metric threads with a nominal diameter of less than 1 mm are standardized in DIN 14. The nominal diameter together with the abbreviation for the thread standard determines the designation of the thread. A thread with the designation M 10 is thus a metric ISO thread with an outer diameter of 10 mm. In the case of fine threads, the abbreviation MF is supplemented by the value for the pitch, e.g. MF 10 x 0.5. A variation of the metric ISO thread according to DIN 13 is the MJ thread, which is mainly used in the aerospace industry.

What other thread standards are there?

The most common thread used in the UK is the British coarse thread BSW with the associated fine thread BSF. This thread type, also known as Whitworth thread, is used like the metric ISO thread mainly for screws, nuts and threaded rods. The Whitworth pipe thread is standardized according to DIN ISO 228 and bears the designation G in combination with the nominal dimension in inches. It is used in sanitary, heating and air-conditioning technology to connect pipes and has also become the common pipe thread in continental Europe and Germany.

A whole set of thread standards also comes from the American region. Comparable to the European standard of the metric ISO thread is the cylindrical Unified National Thread. It knows five different thread standards: Coarse thread (UNC), fine thread (UNF), extra fine thread (UNEF) and thread standards with special pitch (UN/UNS). The thread designation here is composed of the nominal dimension in inches, the pitch and the corresponding abbreviation of the thread type. Other American thread standards exist for various pipe threads. The thread standards NPT and NPTF designate tapered pipe threads, the thread standard NPS a cylindrical pipe thread.

In addition to the international standards, there are other thread standards for special applications. The steel conduit thread with the thread designation PG is often found in the field of electrical installations. The valve thread (Vg) is used for the valves of vehicle tires. For bicycles and mopeds there is a thread standard with the thread designation FG. And wire thread inserts for reinforcement or repair are also defined by their own thread standard (EG).

The types of threads described so far are fastening threads designed to create a connection between two components. In addition, however, there is also the group of movement threads with metric thread standards, whose task is to convert a rotating movement into an axial one. This includes the trapezoidal thread to DIN 103 (Tr), which is used, for example, in lathes or screw presses. The round thread (Rd) to DIN 405 is conspicuous for its curves from the outer and core diameters, which provide special protection against contamination. It is used for valves, gate valves and fittings. And finally, there is the saw thread with the thread designation S and an asymmetrical thread profile, which is designed for high, one-sided loads, e. g. in hydraulic presses.

Thread standards - standardized taps and dies from BAER

At BAER it is important to us that you will always find what you are looking for in our extensive thread repair range, no matter which thread standard you are working with. In our BAER Tools Online-Shop you will find taps and dies according to all the mentioned metric thread standards and international standards in inches. We are happy to be there for you and advise you personally if you have questions about the different thread types and thread standards. Simply contact our customer service and benefit from our many years of experience and the great expertise of our employees. We look forward to hearing from you!