Screw taps for Rd knuckle thread according to DIN 405

At BAER, we want to support you in all your projects, no matter what they are. That is why it is important to us to offer you tapping tools for a wide range of thread standards. This means you can always rely on the consistent quality and precision of BAER screw taps and thread cutting dies, no matter which thread cutting application you are working on. This is why we also include knuckle thread in our long list of thread types for which we always have products in stock. Although it is rarely found outside of its various specialisms, if you ever need threading tools for knuckle thread, you know who you can turn to with confidence.

The knuckle thread DIN 405 is a movement thread

In contrast to many common threads, such as the metric ISO thread, the knuckle thread is not a fastening thread. Instead, it is used as a movement thread. This means that the purpose of the thread is not to enable a fixed screw connection. Rather, movement threads - such as the knuckle thread - are used to transfer movements or forces. This requires different properties than a pointed thread, for example.

The knuckle thread DIN 405 has these characteristics

To enable force transmission and guarantee easy movement, the knuckle thread has very special features. It can be recognised as such at first glance.

The special profile of the round thread

The most striking feature is certainly the profile. It is completely rounded and has no corners or edges. The knuckle thread DIN 405 has a different nominal profile for the outside and internal thread. The difference lies in the rounding radii. For the external thread, these are identical at the tips and at the base of the thread, but they differ for the internal thread thread. The thread angle is 30°.

Thread table for the knuckle thread standard

The thread designation begins with the abbreviation Rd, followed by the outer diameter in mm, rounded down to an even number. The pitch is then specified. At knuckle thread we specify the pitch in threads per inch, as is usually the case with inch threads.

In addition to the thread designation, the table for the knuckle thread also contains an exact value for the outer diameter, the bolt diameter and the diameter for the core hole of the nut. This information is given in mm. The pitch is also listed both in mm and in threads per inch.

An knuckle thread can also have multiple threads

An knuckle thread can have one or more threads. You can recognise a multi-start thread by the fact that the usual thread designation is followed by a P (for pitch) followed by a numerical value.

The knuckle thread is your specialist for these applications

The knuckle thread is used in some very special cases in which it can fully utilise its characteristic features.

This is what characterises the knuckle thread

The round profile has some decisive advantages. Firstly, it proves to be extremely resistant to dirt and mechanical damage. This becomes clear from the very first glance at the knuckle thread. After all, there are no corners or edges where dirt could get stuck. Likewise, what is already round cannot be abraded by wear. The profile therefore remains unchanged even under high physical stress, preventing unpredictable behaviour.

In addition, the knuckle thread is characterised by large clearance and a low notch effect. The notch effect is a physical mechanism that occurs on notched components and puts them under greater stress. This results in accelerated wear, which must be counteracted. The knuckle thread solves this problem once again thanks to the special shape of its profile, which minimises the influence of the notch effect.

With its features, the knuckle thread scores highly in certain environments

Thanks to these special properties, the knuckle thread is therefore used where dirt and mechanical stress are part of everyday life. In this context, it is also referred to as "rough operation", to which the thread can be exposed without excessive damage or high maintenance costs. An important area of application is the construction of railway carriages. Here, the knuckle thread can be found on coupling and brake spindles or on valves and slides. It is also used in mining and by fire brigades.

Caution, risk of confusion: There are different types of knuckle thread

In fact, there is not just one thread standard, but many different ones. The knuckle thread DIN 405 is the standard round thread for general use. There are also other types that differ from the DIN 405 thread in various characteristics and are intended for special applications. For example, there is a standard specifically for use in mining and another for breathing apparatus and diving equipment.

Knuckle thread in the BAER online shop

In the online shop of BAER - the professional screw tap manufacturer - you will find a large selection of screw taps and thread cutting dies. When it comes to taps, you can choose between a set of hand taps and machine taps for use with your stationary drilling or tapping machine. We stock hand taps for both right-hand and left-hand thread. All of our screw tap for knuckle thread are made from high-quality high-speed steel and manufactured with the highest precision. Our thread cutting dies for knuckle thread are best used if you want to cut external threads.

The threading tools presented here are suitable for knuckle thread DIN 405. However, we are also happy to help you if you would like to work with a different standard. In this case, simply contact us and we will find the best solution for you! If you have any other questions, requests or suggestions, you can also contact our friendly customer service team at any time using the contact form.