Which of the following types of fasteners is most commonly characterized by flat-faced ends?

The type of fastener that is most commonly characterized by flat-faced ends is the screw. Screws typically have a flat end that allows for efficient engagement with materials when driven into them. This flat end design facilitates a firm grip and ensures that the screw can be driven in smoothly, allowing for effective fastening.

In contrast, while bolts can also have flat faces, they often feature rounded or tapered ends depending on their design and intended use. Nuts are typically used in conjunction with bolts and have an internal thread but do not have the same flat-face characteristic as screws. Lock washers, on the other hand, are meant to be used with bolts or screws to prevent loosening but do not have a flat end design themselves. Thus, considering these characteristics, screws are indeed the fasteners most commonly recognized for their flat-faced ends.