This is a simple tool I created to help mute piano strings while tuning the instrument. I had a tuning wrench but no mutes so this allowed me to get the job done.
Mutes the outer strings:
Mutes end strings:
It's basically a chopped up eraser screwed to an L bracket, tie-wrapped to an old drum stick.
The L bracket and stick allow you to mute the strings below the hammer which is essential for the higher strings on upright pianos.