When looking at a technical drawing for a custom stud, bolt or screw you might see a note that states that threads are to be ‘cut thread’ or ‘rolled thread’ (this is usually specified either within the drawing notes or next to the thread dimension). This note is critical and communicates how the designer would like the thread to be manufactured.

What is the difference between a cut thread and a rolled thread?

The key differences between a cut and a rolled thread are; a cut thread, also referred to as a machined thread, is created by removing material from a stud, bolt or screw to create the threads. This process is typically done using a single point tool, threaded dies, thread mills or a tap to achieve the desired thread diameter and pitch. As material is removed from the stock, this process can weaken the core body of the respective stud, bolt or screw.

On the other hand, a rolled thread is produced by pressing the thread form into the stud, bolt or screw by passing a bar or blank through flat plates, round dies and other forming tools. This method does not remove any material from the stock.

It must be noted that not all materials are suitable for thread rolling. A brittle material is not always suitable for the manufacturing process of a rolled thread due to the plastic deformation of the material required.

Advantages of a Rolled Thread

The key advantage to a rolled thread over a cut thread is the enhanced fatigue properties. Due to the nature of the thread being pressed into the body and the manufacturing tooling associated in that production method, a rolled thread will have a rad in the root of the thread.

In comparison to a cut thread which will have a sharp ‘V’ cut at the root of the thread, the additional radii in a rolled thread allows for much better load transfer under cyclic loading.

This root radii also increases the bolts cross sectional area compared to a cut thread making a rolled thread slightly stronger in tensile loading as well!

During the forming of a rolled thread, there is some cold working of the material resulting in grain alignment within the material which also contributes to enhanced strength and fatigue properties.

But which one do I use?

In summary, rolled threads can be a great addition to any engineering assembly and the good news is both cut threads and rolled threads can be interchanged.

The vast majority of standard mass produced fasteners are rolled threads, however for custom made studs, bolts or screws you may find that a cut thread will have less limitations, be cheaper and have significantly less lead time (depending on order quantity).

However, for safety critical applications especially those under cyclic loading such as pressure vessels, vehicle suspension or landing gear, rolled threads would always be the way to go!