With some projects, finding a fastener that works with thin or brittle materials can seem impossible. This is where rivet nuts, which are also known as a blind nuts, blind rivet nuts, or threaded inserts, come in. A variation on the standard rivet, the rivet nut has a tubular round, splined, square, or hexagonal body that is internally threaded and counterbored. As a blind fastener, the rivet nut is installed in instances where only one side of the workpiece is accessible, making it incredibly versatile.
The rivet nut was developed by BF Goodrich in 1936 to mount rubber deicing boots to the leading edge of an aircraft wing. Initially, these rivet nuts were sold under the trademark RIVNUT®, but today a wide variety of rivet nut brands exist.
Here are some tips for the use and installation of rivet nuts:
1. Pick the right rivet nuts.
There are two types of rivet nuts: The first is designed to form a bulge on the application’s blind side as the screw, pin, or bolt is tightened. The second is pulled into a sleeve and thus doesn’t bulge like the other type. So how do you know which to use? It depends on your application. Here are some features and styles to consider:
- Wide front-side flange: This rivet nut feature offers a large load-bearing surface to both reinforce the hole and keep the rivet nut from being pushed through.
- Thick flange: This feature can provide spacing and extra push-out strength.
- Countersunk/low-profile head: With this feature, you ensure an installation that is nearly or completely flush.
- Wedge head: Wedges underneath the head keep the fastener from turning in the hole by “biting” into the mating material. This feature is great for soft materials such as plastic, fiberglass, or aluminum.
- Shape: Rivet nuts come in splined, square, hexagonal, and the standard smooth, round cylindrical style. Each style is meant to keep the fastener from turning at high torque levels, especially in softer materials.
- Open or closed: Rivet nuts come in open- and closed-end styles, with the latter preventing water and dust getting into the assembly, such as with an automotive installation.
- Thin or thick wall: Whereas thick wall rivet nuts (also known as standard style) offer keyed heads, thin wall rivet nuts do not.
If you’re not sure what kind of rivet nut you need for your application, seek out a fastener expert so all necessary project variables are met.
2. Use in countless materials.
Rivet nuts are easy-to-install, reliable fasteners that can provide strong load-bearing threads into weak or thin gauge materials such as castings, housings, panels, tubes, and extrusions. Additionally, because of their wide grip range tolerance, rivet nuts can be installed into a variety of material thicknesses.
3. More practical than other fasteners.
Made from aluminum, stainless steel, steel, brass, and Monel, rivet nuts offer a variety of benefits over bolts, self-tapping screws, and pressed inserts. In fact, rivet nuts are not impaired by heat, unlike other fasteners such as weld nuts. Many times, installing rivet nuts is just more practical in comparison to other available fasteners.
4. Perfect for your industry and application.
These fasteners are designed to be automated and are used widely throughout the automotive industry to attach items to dashboards, as well as in the chassis and bodywork to connect roof racks, spoilers, plastic fenders, radiators, and more. Rivet nuts are also perfect for every stage of production with no reworking needed after insertion—even when the workpiece has already been coated or painted. Some other industries and applications:
- Playground equipment
- Office furniture
- Solar panel installation
- Medical technology
- Plastics engineering
- Aerospace industry
- Military vehicles
- Swimming pools
5. Use the right tool.
Among the primary benefits of rivet nuts are that they offer a faster assembly and lower installation costs compared to other fasteners. Because rivet nuts are made to be automated and used in factory settings, power installation tools are often mounted to a six-axis robot. But for individual use, you can install rivet nuts using easy-to-operate and lightweight hand tools or air/hydraulic setting tools. Here are the most popular options:
- “Spin-spin” tool: The rivet nut is threaded onto the mandrel on the pneumatic power tool and then inserted into a hole on the workpiece. When the power tool is activated, the mandrel spins quickly to pull the threaded portion of the shank toward the blind side of the workpiece to form a bulge around the unthreaded portion. When the bulge pushes against the back of the panel, it creates a clamping force to grip the sheet. Once the rivet nut is securely clinched in place, the mandrel spins in the opposite direction to unthread itself from the nut, leaving the rivet nut’s internal threading intact.
- “Spin-pull” tool: Similar to the “spin-spin” tool, an air motor is used to thread the nut onto the mandrel. When the rivet nut is inserted into the workpiece, hydropneumatic pressure is used to pull the mandrel back a set distance in order to set it. Then, the air motor is re-engaged to pull the mandrel out of the rivet nut. These tools are great for plastic workpieces.
- “Pull-to-pressure” tool: This tool works the same as a “spin-pull” tool except that instead of pulling to a specific distance, it pulls to a set pressure. When the fastener is placed into the workpiece, hydropneumatic pressure is used to pull back the mandrel. Then, when the preset pressure is achieved, the air motor backs the mandrel out of the nut. If you are fastening metal or a hard plastic, a “pull-to-pressure” tool is ideal and consistent.