RoMix #3036 brush heads have been "PROVEN" to be the safest and most efficient ever developed for Strong Acid Use by the Concrete industry! Featuring rubberized form plastic blocks with "YOUR CHOICE" of several acid proof fibers. No more cracked of melted blocks as with other brands. #3036 HEADS are "THREADED" to accept any RoMix handle. Sold In Dozen Lots.