GROCO Backing Block f/2" & 2-1/2" Seacocks

The GROCO Backing Block for 2" and 2-1/2" seacocks is a critical reinforcement component designed to distribute the load of through-hull fittings across your vessel's hull. This marine-grade backing block prevents stress concentrations that can lead to fitting failure, water intrusion, or structural damage—problems that become critical when you're miles offshore or in rough conditions where a failed seacock can compromise safety.

Engineered from marine-specific PVC foam, the GROCO backing block offers a 1/2-inch rigid thickness that provides secure installation while remaining flexible enough to conform to minor hull curvature—a practical advantage when working with fiberglass hulls that rarely present perfectly flat mounting surfaces. Unlike wood or composite backing blocks that swell, absorb moisture, and degrade in saltwater environments, PVC foam resists moisture absorption and maintains structural integrity across decades of exposure. The threaded brass inserts press directly into the hull-side mounting holes, matching your seacock flange pattern, while the opposite side spreads the clamping force across a wider surface area.

This backing block suits weekend cruisers maintaining through-hull fittings on cabin drains, head discharges, and raw-water intakes, as well as serious offshore anglers who rely on seacocks for bilge systems and engine cooling. Proper backing-block installation extends seacock service life and reduces the risk of leaks that require emergency repairs at sea. The environmentally friendly PVC foam formulation delivers durability without the ecological footprint of pressure-treated lumber.