Master Lock Trailer Lock Set

The coupler lock in the Master Lock 3794DAT trailer lock set covers 1-7/8 in (48mm), 2 in (51mm) and most 2-5/16 in (59mm) couplers, so a standard 2-5/16 gooseneck or heavy tandem coupler is within range. Note the wording on the largest size: most 2-5/16 couplers, not all, so an unusually shaped or oversized latch housing at that size is the one case where it may not seat.

One key runs all three. The trailer coupler lock, the receiver lock and the trailer coupler latch lock in the 3794DAT set ship keyed alike on a K1 key blank, so the driver carries a single key instead of three, and a spare cut from a K1 blank works on the whole set.

The stainless steel coupler latch lock adjusts from 9/16 in (14mm) up to 2-3/4 in (70mm), so it spans thin flip-latch coupler tongues through to thick cast latch assemblies. That adjustment range is what lets one lock serve a mixed trailer fleet where the latch geometry differs from unit to unit.

A coupler lock alone only stops someone hitching the trailer to a ball. The 3794DAT set adds two other pieces: the receiver lock, which secures your ball mount or hitch accessory in the truck receiver so that gets stolen either, and the latch lock, which pins the coupler latch itself closed. If your exposure is a trailer parked unattended on a job site, you want the coupler plus latch coverage; if it is the hitch and ball mount left in the truck overnight, that is the receiver lock. Buying the set keys all three to one K1 key rather than leaving you with three different keys.

Use the coupler latch lock. With the trailer coupled to the ball, the coupler lock has nothing to occupy, but the latch lock clamps the coupler latch in place and adjusts anywhere from 9/16 in to 2-3/4 in to suit the latch on your tongue. The coupler lock is the piece for an unhitched trailer sitting on its jack, and the receiver lock secures the ball mount in the truck once the trailer is dropped.

Yes, it is listed for marine and offshore security as well as trailers, trucks and towing. The latch lock body is stainless steel, which is the piece that matters at a ramp or a coastal yard. Keep in mind this is a residential-grade auxiliary lock set rather than a commercial security rating, so treat it as deterrence for a parked boat trailer, not as a rated barrier.

The 3794DAT set is supplied keyed alike within itself on a K1 key blank, meaning the three locks in one box share a key. K1 is the common Master Lock consumer keyway, so additional K1-keyed Master Lock cylinders can be cut to a matching key by a locksmith. What the set does not do on its own is guarantee that two separately purchased 3794DAT sets arrive on the same key change, so plan fleet keying around a single set per trailer or have the extras rekeyed to one bitting.