The Difference Between Bolts Screws and Studs

Spend enough time reading about machinery of any kind, and you will see repeated references to things like bolts, screws, and studs. But for the uninformed, these labels can seem interchangeable and vague? What differentiates a bolt from a screw from a stud? In this blogpost, we will explore and define these differences.

According to the Machinery’s Handbook, the primary difference between bolts and screws lies in their purpose. While there are of course exceptions, bolts are used to assemble two or more unthreaded components. When used in conjunction with a nut, the bolt will remain secure, holding the components together and fastening them. Screws, on the other hand, are used with threaded components. This does not necessarily mean that the component or components used with screws must be threaded, as the installation of the screw may create the threading. This is a key difference between the two; bolts must be installed in holes that are unthreaded and must be completed with a nut on one end to be secure, while screws are inserted into holes that have an internal thread or create their own threading. Bolts are tightened by winding the nut further down on the bolt’s threaded portion, while screws are tightened by twisting the head with torque.

Finally, a stud is a metal rod or shaft with threads on both ends. Most studs are long, but the size of course varies depending on the intended purpose and application. Studs do not have a head like a screw or bolt does that can be turned for tightening, and therefore requires a nut at both ends to be fastened.

Bolts, screws, and studs are made from several different metals, including carbon and stainless steel, brass, nickel alloy, and aluminum alloy. What type of metal is chosen depends on the role the fastener will play, and what stresses it will face, like heat, weight loads, corrosion, exposure to chemicals, etc.