Most of the variety of headed fasteners come from the different head types, with the threaded body remaining mostly the same. It follows, then, that headless fasteners only come in a few flavors, three of which will be covered in the course as being the most pertinent to the Automation industry: set screws, all-thread, and headless shoulder screws.
All thread, also known as threaded rod, is the simplest threaded fastener there is. It’s defined by its name, it’s nothing but the thread. All-thread is often sold in long lengths meant to be cut down to a usable size or sold in packs precut to a specified length. Unlike other threaded fasteners, threaded rod has no drive element; there’s not slot or hex drive to turn them. This means that there is no top or bottom, up or down, for threaded rod. In order to retain parts in tension, bearing surfaces must be provided. This is usually done with nuts and washers on both sides to create an all-thread sandwich. Threaded rod is useful when a length is needed that exceeds regularly available sizes of standard fasteners.
Set screws, also known as grub screws or blind screws, are effectively a standard bolt without the head, but unlike threaded rod, they do include a drive portion and a bearing surface. The drive portion is cut into the center of one side as a slot, hex drive, or other standard drive, while the bearing surface on a set screw is the tip of the screw.
This tip geometry varies depending on the purpose of the screw. Common tips include:
When used to retain threaded parts on a shaft, the tip is made to eng