Torque and Thread Cutting or Rolling Screws

Torque and thread cutting or rolling screws

June 10, 2025
By Bob Lund | Engineering Manager

Fastenal provides torque tables for bolts, hex cap screws, socket head cap screws, and more. These tables cover a variety of sizes and grades in both inch and metric product. A common question we receive is: Why don’t we publish torque values for thread cutting or thread rolling screws?

Torque is a force multiplied by a distance. That force is used to overcome friction during installation, to stretch a bolt and create clamping force, and to cut or form threads. All of these actions require torque to overcome resistance forces and properly install the fastener. Let’s explore this further.

When tightening a bolt and nut together, there is friction to overcome in the threads and under the head of the bolt—or the bearing surface of the nut, depending on which is being turned. Additionally, there is an axial force involved that stretches the bolt to a desired clamp load. This stretching is what creates the clamping force required in most bolted joints.

Thread cutting and thread rolling screws also involve torque during installation. These fasteners are typically installed into a pilot hole. The ASME B18.6.3 standard provides tables with suggested starting points for drill bit or formed hole sizes. These fasteners are generally case-hardened, meaning they have a very hard outer shell and a softer core—think of an M&M or a Skittle. The hardened surface is what cuts or forms threads in the mating material.

Before discussing torque values, it’s important to understand the purpose of these screws. Case-hardened fasteners are primarily used as placeholder fasteners. We do not want to stretch a case-hardened fastener during installation or during the loading seen by the product on which it is used. Imagine applying a tensile load to an M&M—it would crack. That’s why it’s critical to use these fasteners only in appropriate applications.

The standard for this type of part (ASME B18.6.3) specifies that these screws are intended for applications where you have at least one diameter of thread engagement, whether in a blind or through hole. While the standard offers guidance on hole sizes, it also recommends testing to determine the optimal combination of hole size and installation torque for each application.

There are many ways to create a hole—drilling, laser cutting, stamping, or forming in a casting, for example. Each method has different tolerances they can hold. Installing the same screw into holes at opposite ends of the tolerance zone will result in different torque requirements. A smaller hole diameter will require higher torque loads to form threads, as more of the screw’s threads engage with the material.

Material thickness (in through holes) or depth (in blind holes) also affects installation torque. Most of the thread formation occurs with the first few threads of the screw. Since the formed threads match the screw’s threads, there’s more friction than in a typical bolt-and-nut setup, where a small clearance is intentionally left for easier assembly. The torque required for thread formation by the first few threads of the screw in a pilot hole is larger than the torque for friction in the trailing threads, but both need to be a part of our testing.

Material hardness also plays a significant role in the torque needed to assemble a thread forming screw. Is the material the threads will be formed in hardened? If the base material is softer than the case-hardness of the thread forming screw (typically HRc mid-40s and up), the screw will be able to form threads in the mating material. Even in non-hardened materials like aluminum, brass, or zinc—which are much softer than steel—the lower the hardness of the mating material, the less torque it takes to create threads.

For all these reasons, it’s not feasible to assign a universal installation torque to thread forming screws. Instead, we recommend testing at each location. To keep it simple, use the actual mating part or a scrap piece of the same material. Drill or form the hole as it would be in production, then install the screw in 5 to 10 locations using a torque tool. Record the maximum torque required to seat the screw flush with the surface. Then continue tightening until failure occurs—either the screw breaks or the threads strip. Your target installation torque should fall somewhere between the seating and failure torque values. Repeat this test whenever any variable changes.

Torque and thread cutting or rolling screws

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