Collar nuts are used in a wide range of workholding applications. Also known as flanged nuts, they are characterized by wide, protruding base. Known as a collar, this protruding base acts like a built-in washer. It distributes the clamping force over a larger area, thereby protecting the workholding components from damage. If you’re planning to use a collar nut, however, you’ll need to choose the right type.
Flat vs Spherical Face
Some collar nuts have a flat face, whereas others have a spherical face. Flat-face collar nuts feature a flat collar end. This is the part that rests against the workholding component. Assuming the workholding component is also flat, flat-face collar nuts provide uniform load distribution.
Spherical-face collar nuts, on the other hand, feature a curved collar end. They are typically used in applications where the bearing surface is also curved. Spherical-face collar nuts provide better contact in such applications, resulting in stronger clamping performance.
Nut Size
You should consider the size when choosing a collar nut. Large collar nuts typically provide better load distribution and support larger bolts. The downside, though, is that they take up more space in workholding assemblies. Therefore, you should check the height and width when choosing a collar nut. Make sure it’s not too big for the space in which you intend to use it.
Thread Size
In addition to the nut size, you should consider the thread size when choosing a collar nut. Thread sizes for U.S. fasteners typically consist of two numbers: the major diameter of the nut and the threads per inch (TPI).
A collar nut with a 1/4 – 20 thread size, for instance, has a major diameter of 1/4 inch and 20 TPI. A collar nut with a 3/4 – 10 thread size has a major diameter of 3/4 inch and 10 TPI.
Finish
Something else to consider when choosing a collar nut is the finish. Like with other fasteners, many collar nuts are designed with a protective outer layer. Known as a finish, it shields the nut from corrosion and physical damage.
Black oxide is a common finish in which collar nuts are made. It involves a chemical conversion process, essentially converting the outer layer to a stable iron oxide. The process involves submerging the collar nut in an alkaline solution. Once submerged, the outer layer undergoes a chemical conversion process, which turns the outer layer into black magnetite, or what’s more commonly known as black oxide.