This is a block of crepe rubber.
Use this to 'clean' clogged belts or disc abrasives when they load up with material.
In use, you push the block of rubber into the clogged belt and the rubber heats up and binds with what ever material has loaded up the abrasive. The rubber grinds pull the material out and fall away like metal or wood dust.
Normally you wouldn't need one of these if you only grind metal as that doesn't load up a belt normally.
Use these if you ever grind (sand) wood, plastic, leather, kydex or other material. It doesn't take much and these will pay for them selves.
