Attwood Marine Standard Straight Barbed Thru-Hull Fitting, 316 Stainless Steel, Above-Water-Line

Overview

The Attwood Marine Stainless Steel Thru-Hull Standard Straight Barbed is a straight hose thru-hull fitting for above-waterline plumbing on boats, offered in hose inner diameters from 5/8 inch to 1-1/2 inch. It is used where a hose needs a clean, secure exit through the hull for drains, bilge discharge, livewell plumbing, or similar topside water-handling runs.

The fitting is cast from enhanced 316 stainless steel, with visible surfaces polished to a mirror finish and passivated for added corrosion resistance. The straight barbed tail gives the hose a positive grip area, while the threaded body, flange, and gasket help create a controlled hull-side installation when paired with the proper marine sealant and clamps.

Key features

• Above-waterline thru-hull fitting for marine hose discharge and drain applications.
• Enhanced 316 stainless steel construction for use in saltwater, spray, and wet deck areas.
• Polished and passivated visible surfaces help maintain a clean exterior look on the hull.
• Straight barbed tail provides room for multiple hose clamps where the installation allows.
• Channel under the flange helps hold a bead of sealant during installation.
• Wrench flats or an end notch help one installer tighten the fitting from inside the hull.
• Full-length standard thread supports installation through thicker hull sections within the fitting size limits.
• Available for 5/8 inch, 3/4 inch, 1 inch, 1-1/8 inch, 1-1/4 inch, and 1-1/2 inch hose inner diameters.

Variants

This range varies by hose inner diameter, with six sizes covering common small-boat and cruising-boat plumbing needs: 5/8 inch, 3/4 inch, 1 inch, 1-1/8 inch, 1-1/4 inch, and 1-1/2 inch. The correct version is the one that matches the inside diameter of the hose being connected, not the outside diameter of the hose or the outside measurement of the barb.

The stainless steel straight barbed construction and above-waterline installation purpose remain consistent across the range. Installation dimensions such as flange diameter, thread outside diameter, thread length, hole saw size, and maximum hull thickness vary by fitting size, so those measurements should be checked for the specific diameter before drilling or replacing an existing thru-hull.

Installation and fit

Use this fitting only for above-waterline locations. Before installation, confirm the hose inner diameter, the hull thickness at the mounting point, the required hole size, and the space available inside the hull for the threaded section, backing hardware, hose bend, and clamps.

The flange should sit flat against a clean hull surface, with suitable marine sealant applied under the flange. The barbed end should be paired with marine hose of the correct size and secured with clamps appropriate for the hose and the service location.

Use cases on board

This fitting is a good match for boat owners replacing plastic above-waterline outlets with stainless hardware, or for builders and refit shops matching stainless thru-hulls to visible topside drains and discharge points. It suits exposed hull areas where appearance matters and where the fitting may see spray, washdowns, UV, and vibration during normal use.

Care and service

During routine maintenance, check the exterior flange, sealant line, hose connection, and clamps for movement, corrosion staining, or signs of leakage. Keeping the fitting rinsed after saltwater use and inspecting the hose connection at the start of the season helps catch installation issues before they become larger plumbing problems.