This set of 3 SandFlex blocks by Klingspor are made in Germany (must be good jah!). Coarse, Medium, Fine.
They are a rubber compound fused into a block with abrasive particles throughout.
Used dry with no water or solvent, they’re ideal for cleaning light to medium rust of various surfaces and leaving a lovely shine. Handplanes, chisels, machine tables, and much more.
They can also work for re-graining stainless steel surfaces like sinks and cooktops.