The mainstay mouse is built up of canvas strips called “parceling” wrapped around the heavy rope, and then covered over with a type of weaving known as grafting. When in use, one end of the rope will pass through an eye in the other end until it fetches up with the mouse, which will act as a sort of stopper in the eye to form a loop.

This is part of the standing rigging, and when seen on Virginia, it is painted black to emulate the tar coating traditionally used on ships.