The Best Trailer Hitch Locks

One lock handles three coupler sizes. Trimax builds the UMAX100 to fit 1-7/8-inch, 2-inch, and 2-5/16-inch couplers, which covers nearly every bumper-pull trailer sold. That matters if you own a boat trailer and a landscape trailer and don't want to remember which lock goes where. Toss it in the truck, and it fits whatever you're towing that weekend.

The body is hardened steel, and the shape does as much work as the metal. There's very little exposed shackle for a cutter to seat on. Popular Mechanics points to hardened boron alloy over plain carbon steel for exactly this reason. It's the difference between a lock that gives up to a two-handed bolt cutter and one that doesn't.

Pick it up and you get it. At roughly five pounds, it's a dense chunk of metal, and that heft reads from across a parking lot. Good Sam makes the point that most trailer theft is opportunistic rather than planned. Someone walking a campground row at dusk isn't defeating your lock. They're looking for the trailer without one, and yours won't be it.

Buy this one if you only buy one. A coupler lock stops the fastest attack, the one where a stranger backs up and drives away inside a minute. A receiver lock protects your ball mount, which is worth a fraction of the trailer. So if you're only getting a single lock, put it on the coupler and stop worrying about it.

Flaws but not dealbreakers

It's heavy and it's awkward. Five pounds of steel doesn't stow neatly in a door pocket, and one-handed operation is a stretch when you're reaching over a tongue jack in the rain. On a small utility trailer with a narrow tongue, it's more lock than the trailer really needs.

The Amazon listing is unusually thin, too. There are no feature bullets, and the page carries a note that the photo is a stock image and actual parts may vary. You're buying on Trimax's reputation more than on anything the listing tells you.

Two locks, one purchase. That's the whole argument, and it's a good one. Plenty of people who own a trailer own two, or they've got a friend's flatbed parked behind the garage half the year. Protecting both usually means paying twice. Here you don't, and the fit range is wide enough that either lock works on either coupler.

Red is a feature, not a color choice. Master Lock finishes these in bright red so they read as a lock from a distance, and that's the point. Good Sam's take on trailer theft is that most of it is opportunistic. Someone crossing a lot at dusk decides in about two seconds whether your trailer is worth the trouble. The color decides it for them.

Master Lock says the lock resists rust and corrosion and that the mechanism resists picking and prying, and the company backs its coupler locks with a limited lifetime warranty. That warranty is a reasonable stand-in for durability evidence when nobody is cutting one open for you. It also means a seized cylinder after three winters becomes the company's problem instead of yours.

Flaws but not dealbreakers

The two locks come keyed differently. Master Lock says so plainly on the listing, and it's the thing that stings. You'll carry two keys and you'll eventually grab the wrong one in the dark. If one key across everything matters to you, shop keyed-alike sets instead.

The build is lighter duty than the Trimax. This is a deterrent lock, not a vault, and someone with a cordless grinder and no audience gets through it. For a trailer parked in a lit driveway, that's fine. For a jobsite trailer full of tools, step up.

Master Lock backs its coupler locks with a limited lifetime warranty.

It's the only thing here that covers the latch. A coupler lock stops someone from hitching up. A pin lock keeps your ball mount in the receiver. Neither does a thing about the latch popping open while you're doing seventy in the right lane. BulletProof's threaded latch lock handles that, and once you've watched a trailer wobble in your mirror, you'll care about it.

The pin is where the thinking shows. It's 5/8-inch with four inches of usable length, so it clears 2-inch, 2.5-inch, and 3-inch receivers, and BulletProof includes anti-rattle spacers for the two smaller sizes. That kills the clunk you hear at every stop sign with a loose ball mount. Small thing. You'll notice it on every drive.

For saltwater, this is the set to look at. BulletProof machines its receiver locks from billet aluminum in the USA specifically to fight corrosion, and both the pin and the coupler lock get heavy rubber caps over the keyway. Rinse the ramp grit off, snap the caps back on, and the mechanism stays workable through a season of launches.

The coupler lock uses a half-inch solid steel bar with a pick-resistant cylinder, and it fits the same three coupler sizes as everything else here. BulletProof rates it medium duty, which is honest labeling. For a camper or a cargo trailer it's plenty. For a jobsite trailer in a rough part of town, you'd want the heaviest coupler lock you can get.

Flaws but not dealbreakers

It's the most expensive option here by a wide margin, and you're buying three locks whether or not you need three. If your ball mount lives in the garage between trips, part of the set just sits there.

Eight pounds of hardware has to go somewhere, too. And the listing doesn't say the three locks are keyed alike, so plan on a small ring of keys unless you confirm otherwise with BulletProof.

Ball mounts disappear more often than people expect. They're expensive to replace, they sit in plain view at the back of a truck, and pulling one takes about four seconds when a clip pin is all that's holding it. A keyed receiver lock ends that. This one drops into the same hole the factory pin came out of.

The steel is the reason to choose this one. Trimax machine-forges the T5 from chrome steel and adds a weather-resistant coating, a clear step past the plated hardware-store hitch pin it replaces. Trailer Life's guidance is to match pin diameter to your receiver class, and the 5/8-inch pin here is the standard size for the heavier tubes.

It weighs about a pound and lives happily in a glovebox. That's the practical case for a pin lock as your second purchase. It's small, so you'll actually keep it with you, and installing it takes no more effort than the pin it replaced. Trimax also lists a limited lifetime warranty, which is rare on a part this small.

Flaws but not dealbreakers

The 3-1/2-inch span is built for wide, heavy-duty receivers. On a narrow tube you can end up with slack, and a loose pin rattles at every expansion joint. Measure your receiver before you order.

A 5/8-inch pin also won't fit the Class I and II receivers that take a half-inch pin. If you're towing a small utility trailer behind a crossover, this isn't your lock.

Trimax lists a limited lifetime warranty on the T5 receiver lock.