A mute about the size and shape of a nickle (hence the nickname). These popular mutes are made by Tourte. The two holes sit over the adjacent middle strings (violin D & A, viola G & D) so that the mute can slide into position when needed. When disengaged, the mute should stay relatively still. Even so, many players prefer to keep these in their case unless the music calls for mutes.
We suggest ordering 2 or 3, as they are easy to lose and fun to lend to stand partners.