GROCO Backing Block f/1-1/4" 1-1/2" Seacocks [BB-2]Backing Block for 1 1 4" & 1 1 2" Seacocks Features: Each size fits multiple seacock sizes Press threaded brass inserts into the hull side of the backing block into the holes that match the seacock flange Rigid 1 2" thickness provides secure installation but is flexible enough to conform to minor hull curvature Will not swell or absorb moisture Made from an environmentally friendly PVC foam specially formulated for marine applications Specifications: