Mechanics and builders use it because it allows them to work on an object without it moving around which makes it easier on them.
What materials can they be used on?
They can be used on any object, because the clamps can hold onto anything.
How is it used?
The vice is usually attached to a table, and it has two jaws that are parallel to each other. Before putting the object in, adjust the jaws to the right size. By turning the handle on the outer end of the vice clockwise, you can make the jaws come closer to each other. The jaw farthest from the table is the one that moves. Then, after the object can be put in between the jaws without falling, tighten the jaws even more so the object will be sure to not move.
What are the distinctive features?
The powerful jaws are the main point of the tool, also the handle on the side that looks like a small metal stick with rounded ends.