GROCO Backing Block f/1-1/4" & 1-1/2" Seacocks

The GROCO Backing Block for 1-1/4" and 1-1/2" seacocks is an essential reinforcement component for any serious boater managing through-hull fittings. This compact yet sturdy accessory protects your investment by ensuring that the fastening hardware for your through-hull valves remains secure and properly supported, whether you're running a cruising sailboat, a center console, or a displacement trawler.

GROCO backing blocks function by spreading clamping forces across a wider area of hull material, dramatically reducing the risk of cracking or delamination around high-stress seacock installations. The engineering is straightforward but critical: without a backing plate, fasteners working against fiberglass or composite hulls can create stress concentrations that fail under vibration, temperature cycling, or the lateral loads generated during rough sea conditions.

Whether you're installing new through-hull seacocks, upgrading aging valves, or reinforcing an existing system during a haul-out, the GROCO Backing Block is a practical addition to any through-hull system without adding appreciable topside weight or bulk. It measures 7 by 1 by 9 inches and weighs just 0.25 pounds, making it suitable for fiberglass and composite hulls.