The Denis Wick DW5511 trombone plunger mute has been made from high purity spun aluminium giving it excellent intonation and the Scotchbrite finish gives it a high quality look.
These mutes are often used in a similar manner to the hat mute where the player manipulates the plunger in front of the bell. This gives you many different effects the sound produced.
These are popular for use in avant-garde music and jazz.