Attwood Marine Thru-Hull Fitting, 1-1/4 in Max Hull, White Polypropylene

Overview

The Attwood Marine 387 Series is a white polypropylene thru-hull fitting for routing a hose through the hull on above-waterline drain or discharge points. This family covers common marine hose sizes from 5/8 in to 1-1/2 in, with each size matched to a specific hose I.D. so the installation can be planned around the existing plumbing run.

The molded thermoplastic construction will not rust, corrode, discolor, or contribute to electrolysis, which makes it useful around saltwater spray and wet cockpit, livewell, bilge, and deck-drain areas. These fittings are for above-waterline installation only and should not be used as below-waterline through-hulls or seacock connections.

Key features

• White polypropylene construction resists rust, corrosion, discoloration, and electrolysis in marine plumbing applications.
• Made for above-waterline hose outlets such as cockpit drains, livewell overflow lines, deck drains, and other non-submerged discharge points.
• Available for 5/8 in, 3/4 in, 1-1/8 in, and 1-1/2 in hose I.D. plumbing, making it easier to match the fitting to the hose already on board.
• Maximum hull thickness is 1-1/4 in across the listed sizes, a key fit check before drilling or replacing an existing thru-hull.
• The white finish works well on many fiberglass hulls and transoms, especially where a low-contrast exterior appearance is preferred.
• The profile allows countersinking where a flush fit is needed and helps reduce streaking below the fitting.

Variants

This Attwood Marine thru-hull fitting is offered in multiple hose-size configurations. The main difference between variants is the hose I.D. each fitting accepts.

The listed variants share the same white polypropylene construction and above-waterline use requirement. Installation hole size, flange diameter, and stem length vary by hose size, so those dimensions should be checked against the hull thickness and the space behind the mounting location before installation.

• 3873-3: Hose size 3/4 in. This size suits small drain or discharge hose runs where a compact thru-hull is needed above the waterline.
• 3872-3: Hose size 5/8 in. This smaller hose size is useful where the plumbing run is tight or where the connected equipment uses a smaller outlet.
• 3874-3: Hose size 1-1/8 in. This mid-size option fits common marine drain and discharge applications that need more flow than the smaller hose sizes.
• 3875-3: Hose size 1-1/2 in. This larger fitting is used for higher-volume above-waterline discharge or drain lines and has a 3-1/2 in stem length.

Installation and fit

Before installation, match the fitting to the hose I.D. and confirm the available hull thickness, exterior flange space, and inside clearance for the hose bend. The 5/8 in and 3/4 in versions use a 1-1/8 in installation hole, while the 1-1/8 in version uses a 1-3/8 in installation hole and the 1-1/2 in version uses a 1-7/8 in to 2 in installation hole.

Use a marine sealant suitable for plastic fittings and the hull material, then tighten the fitting enough to seat it evenly without stressing the flange. Since this is a plastic above-waterline fitting, it should be inspected periodically for UV aging, impact damage, and sealant condition.

Use cases on board

This fitting is a practical replacement for aging plastic thru-hulls on small powerboats, fishing boats, center consoles, runabouts, and sailboats where the discharge point remains above the static and heeled waterline. It is a good match for owners replacing a faded or corroded fitting and wanting a simple white outlet that connects directly to the correct hose size.