A thread insert is a type of fastener component that can serve as an alternative to cutting threads into a material. These components can be cast or molded in place when an object is created, or installed after the fact. Some types of thread inserts can be screwed or pressed into blank holes, while others consist of helical wire threads that must be screwed into place by a special tool. Regardless of the particular design, each different type of thread insert is meant to allow a stud or bolt to be screwed into place.
There are many different types of thread inserts, each of which can be best suited to certain applications and usage with particular materials. Some thread inserts are designed to be incorporated into an object when it is created. One type of fastener component that fits this description is the mold-in insert. These components are placed into molds prior to the injection of plastic so that the finished part will contain metal threads. A similar design is the captive nut, which is a type of thread insert that is typically installed in materials that are too thin to otherwise support fasteners.
Other types of thread inserts can be installed into existing objects or used to repair damaged threads. Self-tapping inserts and press-fit inserts are two types of fastener components that are often installed after the fact. Both of these varieties require that a blank hole be drilled into a workpiece before installation. In the case of the self-tapping insert, the component is designed to be screwed directly into a blank hole. It is also possible to secure this type of thread insert with epoxy.
Press-fit inserts are also designed to be installed directly into blank holes. A hole that is roughly the same diameter of the insert is typically drilled, after which the fitting can be pressed into it. This can often be accomplished with a hammer or clamp, though an arbor press may be needed. Both press-fit and externally threaded inserts are commonly used in woodworking, though they can also be used in other applications.
A type of thread insert that is often used to repair damaged threads is the helical insert. These components consist of diamond shaped wire that is wrapped in a helical pattern. Installation typically involves drilling out damaged threads, tapping the hole and then screwing the coil insert into place. Since the wire is typically diamond shaped in cross-section, it will tend to bite into the threaded hole and provide a stronger hold than might otherwise be possible.