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What is the difference between multi-start threads and single-start threads?

Multi-start thread or single? There are so many confusing terminologies surrounding lead screws, so let’s strip it down and get back to basics.

What is the difference between a single and multi-start thread?

Lead screws are machine elements that convert a rotary movement into linear travel. Lead screws consist of a cylindrical round thread on which a single helix spirals the continuous length, transforming it into a screw. The threads can have, for example, the trapezoidal thread form, metric thread form or the dryspin® geometry designed by igus®. The dryspin® thread is similar in structure to a high helix thread.

Let’s have a look at what constitutes a single threads and a multi-start threads.

multi-start threads and single-start threads?

L = LEAD = Linear travel in mm per one screw revolution
P = PITCH = Spacing from one thread to the next

Single start threads

The lead screw on the left (number 1) shows a single start lead screw. You can identify this by having one single thread. This is what is referred to as a single start. This means that the distance between the flanks, marked by pitch, is also the linear travel (lead) in millimetres per revolution of the lead screw.

Multi-start threads

For lead screw number 2, a further thread has been added, which is shown with the green illustration. This means that with one revolution of the lead screw the two-fold stroke is achieved (lead = 2 x pitch). The start of the thread is offset by 180°, i.e. opposite each other. This is classed as multi-start threads, or sometimes referred to as a two-start thread.

Finally, the third lead screw in this example shows a four-start lead screw. This means we have 4 thread starts indicated by orange, green, purple and blue. For the linear travel the same calculation applies here as for the other examples.  The linear travel (lead) is therefore four times the distance between the flanks. The start of the thread is at a position of 90° to each other.

For more information about lead screws, multi-start threads and single-start threads, read more blogs here

Which thread is best for your application?

Deciding whether to use multi-start threads or single for your application is sometimes tricky, simply because there are advantages and disadvantages to both. For example, a single start trapezoidal thread will self-lock, whereas a multi-start thread will not. On the other hand, you can travel much faster with a multi-start thread.

Our experts are on hand to offer application advice, to ensure that the best possible thread choice is used in your application.

If you need further information on an of our leadscrews, please visit the website https://www.igus.co.uk/info/lead-screw-units-lead-screw-units or speak to one of our experts on 01604 677240.

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