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Rolled Vs Cut Thread Bolts Irrespective of whether we’re talking about headed bolts, bent bolts, or rods, threads constitute a mechanical fastener that is produced by rolling or cutting. As its name suggests, roll threading implies introducing a hardened steel die between the diameters of the finished thread. The dies penetrate the blank space, leading […]

Rolled Vs Cut Thread Bolts

Irrespective of whether we're talking about headed bolts, bent bolts, or rods, threads constitute a mechanical fastener that is produced by rolling or cutting. As its name suggests, roll threading implies introducing a hardened steel die between the diameters of the finished thread. The dies penetrate the blank space, leading the newly formed thread roots outwards to create the crests.
cut thread and rolled thread comparison
Photo credits: www.learneasy.info
On the other hand, cut threading entails removing the material from a round bar of steel to form the threads. While technically both processes yield the same results, the main distinctions between the cut threads and rolled threads bolts reside mostly in the manufacturing process. Let's elaborate.

Rolled Thread Bolts Have Smaller Bodies

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With the cut threading process, manufacturers can obtain a bolt with a full one diameter body and one diameter threading, whereas the rolled threading reduces the fastener's body to only .912 inches, while maintaining the threading to one inch diameter. This is why some engineers argue that a bolt with a reduced body is weaker than its full sized counterpart.
However, it is necessary to mention that the strength of the fasteners lies in the threading and not its body size. Because the weakest area of any mechanical fastener resides in the minor differences of the threads and both processes can provide identical threads, you can understand why this belief is nothing more than a misconception.

 

Cut Threading Leaves Behind Tiny Tears

If you were to put two bolts obtained via roll threading and respectively cut threading side by side and analyzed with a magnifying glass, you will notice that the latter presents tiny tear marks. Cut threading tends to tear the material, leaving a set of marks that run perpendicular to the direction of the thread and that travel into the fastener's body. Unfortunately, the minor fractures made by the tool cutting the thread can, and in most cases will, grow over time threatening the bolt's stability.
Opposite to the cut threading process, roll threading deforms and cold works the material, thus adding to its innate endurance. Not only does the hardened steel die add to the bolt's resilience and strength, but the process doesn't leave any tears that can later on transform into cracks.

Rolled Thread Bolts Cost Less

The main advantage of the cut threaded bolts is that they can be manufactured to all specifications, as there are few limitations with regards to diameter and thread length. Without denying that cut threading could be invaluable for manufacturing special fasteners for sensitive pieces of equipments, let's not forget that the process implies significantly longer labor times and the implicit higher costs.
Opting for rolled thread bolts means shorter labor times and substantially lower costs. The lower cost of roll threaded bolts also comes from the smaller body diameter; a smaller body means less weight and consequentially, less materials and resources used for heat-treating, galvanizing, plating, so on and so forth. Moreover, the burnishing effect of the rolling makes the bolts smoother, while the cold working makes them overall more resilient to damage.

About the Author

Larry Melone
By Larry Melone
President

Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.

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