Which type of fastener is characterized by being cylindrical with external threads?

The correct choice is a screw. A screw is a type of fastener that features a helical ridge known as an external thread wrapped around a cylindrical shaft. This thread design allows the screw to penetrate materials when turned, effectively securing two or more components together.

In contrast, nuts typically have internal threads and are used in conjunction with screws or bolts to create a tighter assembly. Washers serve primarily as flat discs placed under fasteners to distribute load or prevent damage to surfaces, but they do not possess threads. Bolts, while also cylindrical with external threads, usually have a distinct design where the threaded portion is intended to be inserted through a hole in an assembly and secured with a nut rather than being primarily designed to penetrate materials by rotation like screws do.