Groco Marine Products 1 1/4 High Speed Thru-Hull Fitting with Nut video accessory

Marine bronze thru-hull fitting

This Groco fitting provides a 1-1/4 inch bronze through-hull connection for marine plumbing systems. The high-speed design reduces drag while increasing flow compared to standard thru-hulls. It includes a securing nut and uses C83600 bronze for corrosion resistance. The combined NPSM and NPT threading offers flexible installation options.

Flow capacity and installation limits

The 1-1/4 inch hose size suits waste, washdown or livewell circuits that need generous volume. Bronze construction handles saltwater exposure but adds weight that may require hull reinforcement on smaller craft. The high-speed profile reduces drag at cruising speeds yet cannot eliminate turbulence in tight bends or long hose runs. Installers must verify hull thickness and deadrise angle before cutting the hole.

Bronze build and thread implications

C83600 bronze resists galvanic corrosion when bonded to a vessel's grounding system. The dual NPSM/NPT thread accepts both straight and tapered pipe fittings, so installers can choose hose barbs or threaded valves without adapters. The included nut secures the flange from inside the hull, but access to the interior surface is required for tightening. Bronze threads gall if forced, so lubricant and hand-tightening followed by a light wrench turn are standard practice.