GROCO Block f/3/4" & 1" Seacocks Backing. Backing Block for 3/4" & 1" Seacocks Specifications for GROCO Backing Block f/3/4" & 1" Seacocks: Manufacturer: GROCO Color: Black Features of GROCO Backing Block f/3/4" & 1" Seacocks 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 Package Contents: GROCO Backing Block f/3/4" & 1" Seacocks GROCO BB-1: Block f/3/4" & 1" Seacocks Backing