Xtra Life brand Abrasive Cleaners with wood handle.  Xtra LIfe # 307.  The block measures 1 1/4 x 3.  Overall length with the handle is 7".

Xtra Life Abrasive Cleaners remove wood, metal, fiberglass, autobody filler & most other materials that clog abrasives.  They can be used on both hand held & stationary sanders.