How Hitch Locks Work

Car towing motorcycle on highway.
Hitch locks help protect your cargo by fusing your trailer hitch and receiver together, preventing thieves from making off with your stuff.
Nick Tzolov/

It's race day at your local speedway, and you've got your motorcycle ready for some high-octane knee-dragging. Your pickup truck is towing a trailer with the motorcycle secured on top. Once you arrive at the track, you go off for a while to visit with some friends. When you come back, your truck is there, but the trailer - and your motorcycle - are gone.

Nothing ruins a good weekend of racing (or a good weekend in general) like having your entire rig stolen from under your nose, but it can happen. Fortunately, there is towing equipment available to prevent incidents like that from happening.


Hitch locks are designed to stop thieves from stealing your trailer. A hitch lock keeps your trailer hitch and the receiver together until you unlock it, often with a key. These locks prevent anyone from lifting the receiver, and they won't be able to un-hitch the trailer unless the lock is off.

In this next section, we'll discuss the many different types of trailer hitch locks, and which of these hitch accessories are right for you.


Choosing Hitch Locks

A car towing a trailer on a rural road.
Different classes of hitch locks provide the strength to haul cargo weighing up to 15 tons.
Jill Fromer/

There are a wide variety of hitch accessories available to keep your trailer secure. They come in different shapes and sizes and can be placed on different parts of the trailer and receiver hitch, but their function is the same: to keep your stuff from being stolen.

Receiver hitch locks fit crosswise into a hole on the receiver connected to your towing vehicle. They're used to lock whatever you're towing into the hitch so they can't be separated without a key or number combination. These are usually metal pins with locks on the ends. Some have two locks on either side, and some have a crooked end that prevents them from being pulled out.


Hitches are divided into different classes based on how much weight they can tow safely. They range from Class I, which can haul about 2,000 pounds and could be pulled by small cars, to Class V hitches that can easily tow 30,000 pounds or more and should only be pulled by heavy-duty pickup trucks. To learn more, take a look at How RV Hitches Work.

You'll want to make sure the lock you purchase fits your trailer, hitch receiver and other towing equipment. The most common trailer locks are half-inch and five-eighths of an inch in diameter. Class II receiver hitches use half-inch pins. Class III, IV and V receiver hitches use five-eighths inch pins [source: Trimax Locks]. You must make sure your lock matches up with what you're towing.

What happens when your trailer is unhitched from your vehicle? What if someone were to try and tow it away while it's sitting in your driveway? For that, you'd want a coupler lock. These U-shaped locks fit over the coupler on the trailer's tongue and prevents someone else from hooking up his vehicle to your trailer. Many have ball-shaped tops to go where the ball unit on your vehicle would normally go into the coupler. In short, this prevents another vehicle from hitching up to your trailer.

In addition, there are locks that fit over the wheels of your trailer that prevent them from being moved. These work on the same principle as the "boots" that get placed on the wheels of your when you get traffic tickets - with a big hunk of metal sitting on the tire, that trailer won't be going anywhere [source: Trailer Keeper].

In the next section, we'll show you how easy installing a hitch lock can be.


Installing Hitch Locks

A truck towing a trailer.
You don't need to go to a professional to install a hitch lock.
Steve Shepard/

Keeping your trailer safe from thieves is a relatively easy task, one that requires a lot less labor than some of the tasks involved with hooking up and towing a trailer.

Receiver hitch locks are designed to fit crosswise into the receiver of your towing vehicle. They slide into a designated hole when the trailer hitch is hooked up and then lock in place. The pin slides between both the receiver and the trailer tongue inside it [source: Bear's Truck Accessories]. Typically, you remove a rubber cap at the end which hides the keyhole, insert the included key, and then turn to lock or unlock the pin.


To use most coupler locks, you must insert the key to remove the top bar, open the coupler, place the ball-shaped top inside, lock the coupler, put the top bar back on, and lock the bar in place. With the lock in place, no one will be able to hook up to your trailer.

For more information about using towing equipment properly and keeping your trailer and hitch accessories safe, please see the links on the following page.


Lots More Information

Related HowStuffWorks Articles

More Great Links


  • Bear's Truck Accessories. "What Size?"
  • "Valley Universal Trailer Coupler Lock."
  • Trailer Keeper. "Trailer Security Tip."
  • Trimax. "SXT3 Premium 100% Stainless Steel 5/8" Key Receiver Lock." _Premium_100_Stainless_Steel_5_8_Key_Receiver_Lock.htm