Two prongs for stability. Primarily a practice mute but also good for ensemble playing. Mid to heavy muting.

What Should I Look For in a Mute?
All string players should have at least one mute, and there are three important factors to consider. First and foremost, ease of use. How quickly can the mute be put in place or removed? How important is this to you? Orchestral players sometimes only have one measure to install or remove a mute. Secondly, sound quality. The goal of the mute is to lower the volume only, not dampen the good quality of your instrument. Regarding overall sound quality, the degree to which a mute "rattles" when not in use but still on the strings between the bridge and tailpiece is important as well. Third is aesthetics. Truth be told, many players consider the importance of overall look and feel, trying a variety of mutes to find out what works and looks best on their instrument. Fortunately, mutes are not too expensive, so this is a relatively low cost endeavor.