Which specialized bolt features a square neck?

A stud is indeed characterized by its unique design that includes a square neck. This special feature helps to prevent the stud from turning during installation, allowing for easier tightening and securing of nuts on opposite ends. The square neck provides a larger surface area for the wrench to grip, which enhances the assembly process and improves torque application.

In contrast, the other options do not feature a square neck. A hex bolt typically has a hexagonal head for wrench gripping but lacks the specific square neck design. A cap screw is similar to a hex bolt but often has a fully threaded shaft and is designed to be tightened with a nut. A shoulder bolt, which includes a machined shoulder, is used to create a pivot point or as a spacer, and does not have a square neck either.