Master Lock Universal Lock Trailer Coupler Lock

The 379DAT universal coupler lock covers the three common ball sizes: 1-7/8 inch (48mm), 2 inch (51mm), and most 2-5/16 inch (59mm) couplers. The wording on the largest size matters, most 2-5/16 couplers take it but not all, so if your coupler is an oversized or heavy-duty 2-5/16 casting, measure the latch opening before you commit. The 1-7/8 and 2 inch sizes are a straight fit.

One part number covers the fleet. The Master Lock 379DAT is a universal coupler lock spanning 1-7/8 inch, 2 inch, and most 2-5/16 inch couplers, so a property manager or contractor running utility trailers, dump trailers, and equipment trailers with different ball sizes can standardize on the single model rather than stocking three. It ships as one model, 379DAT, with no size or finish options to pick.

A coupler lock like the Master Lock 379DAT blocks the coupler socket itself so nobody can drop your unhitched trailer onto their ball and drive off. That is theft prevention while the trailer is parked and detached. A hitch pin or receiver lock does a different job, it secures the ball mount into the tow vehicle's receiver so the mount cannot be pulled out. They protect two different points, and a lot of fleets run both. The 379DAT is the coupler side.

Rust and corrosion resistance is built into the 379DAT, and Master Lock lists it for marine and offshore security as well as trailers, trucks, and towing. That is the use case that kills cheap coupler locks, a boat trailer sitting at a ramp or a yard lot through a winter of road salt. Expect it to keep working outdoors rather than seizing after a season.

The 379DAT uses an advance locking mechanism that resists picking and prying, which is the realistic attack on a parked trailer, someone working the cylinder or getting a bar into the body. That is the security claim on this model. It is a residential-duty product rather than a commercial-rated one, so treat it as deterrence for a driveway, yard, or job site, not as a substitute for a locked and gated compound.

No tools, no install. The 379DAT is built to go on and come off by hand, which is what you want on a trailer that gets hitched and unhitched daily by different crew. The trade-off is that it only protects the trailer while it is fitted, so it lives with the trailer, not in the truck.

Order model 379DAT. It is the single configuration of Master Lock's 370 Series universal coupler lock, with no handing, size, or finish choice to specify, so the part number alone completes the order.