Blind rivets are high-performance fasteners that are long-lasting and can be set from one side of a joint. They are easy to install and form a tight, permanent bond that resists vibration and corrosion. That’s why blind rivets are widely used in a variety of industries, from agriculture to automotive to consumer electronics. However, as with any type of blind bolt or rivet, to get lasting performance you have to use the right materials and the right blind rivet size.
A blind rivet, sometimes called a pop rivet, is comprised of a tubular sleeve, which makes up the rivet itself, and a thinner mandrel that fits through the sleeve. When the mandrel is pulled, the mandrel head is pulled into the rivet body to form a secondary head or bulge on the blind end, thus riveting the two pieces together. Blind rivets can be made of stainless steel, steel, aluminum, copper, nickel-copper, zinc, and other materials, sometimes mixing different materials for the rivet and the mandrel. You want to select a rivet material that matches both sides of the workpiece, and you want to be sure that the blind rivet size is right for the hole and thickness of the material.
The Basics of Blind Rivet Size
When choosing the right blind rivet size for the job, there are multiple specifications that you have to consider:
- Hole size – Blind rivets are installed in pre-drilled holes, and you want to be sure that the rivet diameter matches the hole for a snug fit. If the rivet is too small, the joint may loosen or the gap between the rivet and the sides of the hole might allow the blind head to expand in the space between the two workpieces. If the fit is too tight, it is difficult to properly place the rivet. Blind rivet sizes range from micro rivets on up and are available in both standard and metric units.
- Grip range – The grip range is based on the length of the rivet and needs to match the grip, which is the thickness of the materials being joined. Most rivets have a grip range from a minimum to a maximum thickness that will provide an optimal joint. If the rivet is too long, the blind head won’t bind tightly to the blind side of the material; too short, and the head may not form on the blind side at all.
- Desired joint strength – The strength of the joint is determined by both the tensile strength and the shear strength of the blind rivet. When choosing the rivet size, you want to make sure the material and diameter are sufficient to withstand the load along the length of the joint, i.e., it has enough tensile strength. You also want to be sure that if the two parts of the joint material try to slide apart, the rivet has sufficient shear strength that it won’t break. For example, heavy-duty applications, such as railway cars, mining equipment, and agricultural equipment, require stronger joints.
- Desired joint thickness – There are occasions when the thickness of the joint may vary, such as when you are joining different materials, when dealing with curved surfaces, or when pre-drilled holes may be difficult to align. For these applications, you may want a multi-grip rivet with a wider grip range to accommodate the variable joint thickness.
- Primary rivet head shape and size – The primary rivet head size on the visible side of the joint will vary based on the application. The head needs to be sufficiently wide that it won’t pull through. For example, you can use small heads for hard materials such as steel, but may need a broader head size for softer materials such as plastic. The shape of the head also will affect the grip and the look. There are domed rivet heads that provide a good grip and countersunk heads that lie flush with the material but may need to be wider to guarantee against pull-through. There are a variety of blind rivet heads, each useful for different applications.
- Mandrel head size – Just as the primary head has to be sized for the job, so does the mandrel head on the blind side. Once set, the bulbed head formed on the blind side should create a flange wide enough to provide a strong hold and relatively flush with the workpiece. Soft materials such as plastics will require larger flange heads.
- Match the materials – A final and vital consideration is matching the blind rivet size to the materials being fastened together. If you are fastening hard and soft materials together, for example, the head sizes need to match the materials; you can use a smaller head for the harder materials but may need a larger head for the soft side. Sometimes you can use grooved rivets, which have rings that expand and will bite into materials such as wood or plastic when tightened. You also may want to use T-Lok® or peel-type rivets that peel into three or four legs on the blind side to create a strong bind that won’t pull through software materials.
These are just the basic specifications to think about when choosing the right blind rivet size and materials. There are other variables as well that you may want to consider, depending on the application. If you aren’t sure what type or size of blind rivet best suits your needs, check out The Essential Guide to Blind Rivets or contact one of our fastener experts. They will be more than happy to help.