These are awesome metal tool cleaning and polishing blocks. I always have a few around the shop.  Their uses are endless but I mainly use them like an eraser to clean off surface tarnish and light rust from my planes, chisels, and other metal tools. 

They are made of a semi flexible rubber compound with silicon carbide abrasive grits impregnated throughout the entire block.  I prefer the Medium grit (green) for most of my tool cleaning chores.

• Available in three grits - Fine, medium, and coarse.

• Each block measures 3-1/4" long x 2" wide x 3/4" thick. 

• Made in Germany.

• You can "carve" the block into any shape to clean up a concave or convex surface

• As you use it new grits are exposed - it never dulls!