T-H Marine Garboard Drain Plug, 1/2-Inch NPT Brass

The garboard drain plug is one of those small brass parts you never think about until the day it fails. This is T-H Marine's 1/2-inch NPT threaded brass garboard plug, the fitting that seals the lowest drain point of your transom while you're on the water. Pull it on the trailer and the boat drains dry. Thread it back in before you launch and you're buttoned up.

The garboard is the lowest seam of the hull, right where the bottom meets the transom. That's why the drain lives there. Gravity does the work. When your boat sits nose-high on the trailer, every bit of rain, washdown water, and bilge seepage runs straight to that corner and out through this plug. Threaded for 1/2-inch NPT, it matches the most common garboard opening on aluminum and fiberglass hulls, so it fits a huge range of bass boats, jon boats, runabouts, and center consoles.

Brass is the right material here, and not by accident. Down at the waterline a drain fitting takes a beating. Standing water, salt, trailer grit, the occasional knock from a dock line or a boot heel. The machined brass body shrugs off corrosion far better than plated steel, and it won't swell or crack the way a cheap plastic plug does after a few seasons in the sun. It threads smoothly, seats tight, and backs out clean next spring.

A quick word on thread size, because it trips people up. NPT stands for National Pipe Tapered, and the 1/2-inch call-out refers to the nominal pipe size, not the diameter you measure across the threads. The external thread actually measures a bit larger than a half inch. If your existing drain takes a 1/2-inch NPT plug, this one threads right in. If you're not sure, back out your old plug and match the thread. Most trailerable boats built in the last few decades use this exact size.

Installing it is a five-minute job. Wrap the male threads with a couple turns of Teflon tape or lay down a bead of marine thread sealant, then thread the plug in hand-tight and snug it with a wrench. Don't gorilla it. NPT threads seal on the taper, so a firm turn past hand-tight is plenty. Over-torquing brass into a transom fitting is how you crack a fitting or gall the threads.

Here's the habit that saves boats. Pull the plug every time you pull the boat. Leave it out while the rig sits on the trailer or in storage so water drains and air moves through the bilge. That goes double over winter, when a sealed hull traps moisture and any water left inside can freeze and do real damage. Keep a spare in the glovebox too. A garboard plug is cheap. The tow-out when one vibrates loose at the ramp is not.

Run it in salt or fresh, it doesn't care. Brass handles both. After a salt day, a quick freshwater rinse of the transom and the drain keeps everything moving freely, and a dab of waterproof grease on the threads once a season means the plug never seizes in the fitting. Small maintenance, long life.

If you're staring at a corroded, rounded-off, or missing plug, this is a straight replacement for the standard 1/2-inch NPT garboard drain. First-time owner or lifelong angler, it's the same simple part, and getting it right means a dry bilge and no surprises at the launch. We keep these on the shelf because they're the kind of thing you always want one more of.

That's really the whole job. A good garboard plug seals when you want it sealed and drains when you want it drained, season after season, without you ever thinking about it. This brass plug does exactly that, and it's priced so you can grab two.