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Master Lock 389DAT Universal trailer Coupler Lock

Master Lock 389DAT Universal trailer Coupler Lock

Keep Your Trailer Secure From Theft With the Master Lock 389DAT Coupler Lock

Trailers are a tempting target for thieves looking to quickly hitch and tow one away. Without adequate security, you could return from a job site or camping trip to find an empty spot where your trailer once sat. Don’t learn this lesson the hard way. The Master Lock 389DAT Universal Trailer Coupler Lock provides reliable protection to secure your trailer from tow away theft.

Constructed from weather resistant zinc and laminated steel, this compact coupler lock resist picking, prying, hammering, cutting, and other break in attempts. The advanced locking mechanism exceeds industry standards for security. It installs in seconds without tools to keep your trailer coupling guarded.

With durable construction and easy convenience, you’ll have peace of mind knowing your trailer will be where you left it. Keep reading to learn why the Master Lock 389DAT is a smart investment to protect your valuable assets.

About Master Lock

For over 95 years, Master Lock has delivered reliable, quality security products for consumer and commercial use. Based in Milwaukee, Wisconsin, they manufacture a wide range of padlocks, door locks, safety locks, trailer coupler locks and more.

Master Lock rigorously tests and inspects their products to ensure they withstand real world conditions from extreme cold to searing heat. Their padlocks famously pass demanding durability tests including gunfire, sawing, and sledgehammer blows. You can count on Master Lock locks to keep your valuables secured.

Overview of the 389DAT Coupler Lock

Constructed from weatherproof zinc and laminated steel, this lock is built to survive the elements. The advanced locking cylinder provides excellent pick and pry resistance thanks to the special keyway design. It’s conveniently keyed alike to work with other Master Lock products you may own.

Designed to fit 1-7/8″ and 2-5/16″ coupler sizes standard on most small to mid-size trailers, it locks onto the coupler knuckle with a twisting motion when not in use. This prevents a ball hitch from connecting and towing away your trailer.Installation takes literally seconds.

What’s In the Box

The 389DAT ships with everything you need to get started:

  • Master Lock Coupler Lock
  • (2) Keyed Alike Keys
  • Usage Instructions

No tools are required for installation.

Key Features and Benefits

  • Guards Against Theft: Secures trailer coupler to prevent tow away theft when locked. Provides visible deterrent.
  • Durable Construction: Laminated steel and zinc body withstands weather exposure and resists corrosion.
  • Pick/Pry Resistant: Advanced locking cylinder technology foils break in attempts.
  • Universal Fit: Fits 1-7/8” and 2-5/16” coupler sizes found on most small to mid-size trailers.
  • Matches Other Locks: Keyed alike with other Master Lock products for convenience.
  • Easy Installation: Locks onto coupler without tools in seconds when not trailering.
  • Compact Size: Fits in pocket when not protecting your trailer coupler.

Key Specifications

  • Dimensions: 3.94” x 2.99” x 2.99”
  • Compatibility: 1-7/8” and 2-5/16” trailer couplers
  • Body Material: Weatherproof zinc and laminated steel
  • Weight: 0.55 lbs
  • Keyed Alike: matches other Master Lock combinations

Choosing the Right Trailer Coupler Lock

Here are key factors to evaluate when shopping:

Locking Mechanism

  • Clamp locks attach to trailer coupler like a vice to prevent hitching. No modifications needed.
  • Ball locks insert into coupler opening, secured by a cover that prevents ball insertion.
  • Shackle locks use a heavy padlock shackle through the coupler knuckle.


  • Solid steel or thick zinc stands up to prying tools and cutters. Avoid thin aluminum.
  • Laminated steel adds layers for extra strength.
  • Look for weatherproofing if exposed to elements.

Universal vs. Fixed Fit

  • Universal adjust to fit standard coupler sizes, but may have some play. Convenient for multiple trailers.
  • Fixed locks tailor to an exact coupler size for very snug fit, but only work on one trailer.

Pick/Pry Resistance

  • Discourages smash and grab type break-ins. Look for advanced locking cores.
  • Critical for lightweight locks vulnerable to manual attacks.

Keyed Alike

  • Convenience of using existing keys you have on hand for other trailers or locks
  • Avoid dealing with multiple keys


  • Quick, tool-free installation ideal for convenience and ease of use.


  • Highly visible locks deter opportunistic thieves from targeting your trailer
  • Bright colors, unusual shape draws attention

Price Range

Expect to pay $20 to $75+ depending on lock type, size, and durability

Brand Reputation

Look for reliable security names like Master Lock, Reese, and Bulldog.

Customer Reviews

Verify real-world performance and fit from actual owners.


1-year minimum coverage gives assurance on defects.


How do you install the Master Lock 389DAT coupler lock?

Just insert into the coupler opening and twist 90 degrees to lock in place. Reverse to unlock. Takes just seconds with no tools needed.

What coupler sizes will the 389DAT lock fit?

It’s designed to fit 1-7/8″ and 2-5/16″ coupler diameters commonly found on most small to midsize trailers. Very large 3″ couplers may not work.

How effective is the pick/pry resistant design?

The advanced locking cylinder makes manual picking very difficult and foils smash and grab break-ins well. Provides serious theft deterrence.

Does weather affect the lock?

The zinc and laminated steel construction resists corrosion and keeps the mechanism operating smoothly despite exposure to rain, snow, and extreme temps.

Can you get duplicate keys made?

Yes, any locksmith can duplicate your 389DAT keys if needed, since it uses a standard keyway. Keeping a spare key handy is recommended.

Will the lock work on U-Haul or rental trailer couplers?

It depends on the specific coupler size, but generally rentals use very standard 1-7/8” or 2-5/16” couplers that this lock is designed for.

Does Master Lock offer a model with a LED key?

Not currently on this particular coupler lock model, but some of their padlocks and door locks do feature LED key variants.

What if I lose the provided keys?

You can call Master Lock customer service with proof of purchase and they can provide replacement keys matched to your lock’s combination.


The Master Lock 389DAT coupler lock is a must-have for securing your trailer from thieves when parked. The included keys make it convenient to lock up your trailer in seconds whenever you unhitch. Constructed for durability and highly pick/pry resistant, you get serious theft deterrence without breaking the bank. Invest in total peace of mind on your next camping or work trip. Your trailer will be right where you left it.

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