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  1. Trailer Coupler Locks
  2. Master Lock
  3. Latch Lock
  4. Keyed Unique
  5. 7/8 Inch Span
  6. Universal Application Lock
7/8" Wide Trailer Coupler Latch Lock by Master Lock

7/8" Wide Trailer Coupler Latch Lock by Master Lock

Item # 2878DAT
Our Price: $13.63
You Save: 14%
Trailer Coupler Locks
Shipping Weight: 0.34 lbs
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Great Prices for the best trailer coupler locks from Master Lock. 7/8" Wide Trailer Coupler Latch Lock by Master Lock part number 2878DAT can be ordered online at or call 1-800-940-8924 for expert service.
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  • Reviews (47)
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Master Lock Trailer Coupler Locks - 2878DAT

  • Latch Lock
  • Keyed Unique
  • 7/8 Inch Span
  • Master Lock
  • Universal Application Lock

  • 7/8" Shackle fits most popular trailer coupler latch widths
  • Covered keyway resists moisture, dirt, and corrosion
  • Hardened steel construction
  • Removable Python cylinder
  • Ergonomic handle for easy installation
  • Limited lifetime warranty

2878DAT - 7/8" Wide Trailer Coupler Latch Lock by Master Lock

Video of 7/8" Wide Trailer Coupler Latch Lock by Master Lock

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Master Lock Trailer Coupler Latch Lock Review

Hey everybody, Ryan here at etrailer. Today we're gonna be taking a look at the master lock trailer coupler lock. So I know whenever I have a trailer in storage or maybe even parked out in front of my driveway the security of it is always one of those things that's kinda in the back of my mind, you know what's really gonna prevent someone from backing up to it, hooking up and running off with it. And using a coupler lock like this, is just something small that you can do to prevent that from happening. So the way this coupler lock works is really straightforward and simple. What you would do to use it is take your latch your coupler latch, and place it in this position down that way you're not able to get a ball attached to the coupler itself.

And then what you would do is open up your lock. So you're just gonna have a traditional lock mechanism there. You're gonna turn the key about half a turn. That pen is going to open up and give you the space you need to put it on your coupler. One thing I honestly like about this one is that this piece here, this pen, you can't pull it out and separate it from a lock itself.

So everything's got to stay together and you're not gonna have to worry about losing that. Some of the other types when you unscrew them, they come into pieces. And after a while of use it can be a little challenging to get back together, or you know, you set one piece down, drive away and end up losing it. So that's not the case with this one. With that being said, though what you're gonna do is just take the block, push that pen through the hole there in your coupler latch, take your key and lock it back down.

And that's gonna prevent it from opening up. That way, no one's able to open up your latch down here and be able to connect a ball to it. So really simple design, but very effective. So the lock itself is going to have a seven, eight seven inch span. So what that means is the opening there is gonna be seven, eight, seven inch.

So as long as you're a coupler latch for the hole is isn't wider than that this is gonna work with it. And that's a pretty common size if you will. So generally speaking all of your more or less common type latches and couplers like this this will work with it. So as long as that width isn't exceeding that seven eights you're gonna be able to put it around there and lock it down. One thing I did notice once the lock is actually around the coupler, even on a kind of a more narrow style latch like this you're not gonna have a ton of space. If you push it all the way over to get to that pen that's actually keeping everything locked. And that's important because it's really gonna make it difficult to get this removed without the key. So just kinda thinking right off the top of my head. If someone we're to wanna try to bust us off, chances are pretty good they're probably gonna have some bolt cutters, right So I would find it very difficult and hard to believe that even a small set of bolt cutters could manage to get into a space that tight to do any damage. Now granted, that's not to say that this is bulletproof by any means. I'm sure if you really wanted it off you could find a way. You know you might be able to get a saw blade or something in there and chop that, but with that being steel it's gonna be difficult. And I mean, to be honest, if someone's up to no good and out looking to do something like this, chances are good they're not gonna be spending a whole lot of time making a bunch of noise, you know, throwing sparks from cutting metal to get this removed. So one little thing I do like is the fact that this pen handle here is spins. You know, every trailer is set up a little bit different. And so, you know you might need to position this a different way to be able to remove that pen or pull it out once you unlock it. Does have this cap on there to help keep out you know, moisture and things like that. Chances are good if you're using this trailers price sitting for a little bit. So, that's nice. The lock mechanism itself does operate smooth. You know, it doesn't really bind up. I've had experience with some of these similar coupler locks where everything's just kinda rough and gritty almost. That's not the case with this one. It won't take any effort. You know, the pen comes out with ease and it goes back in pretty easily as well. And the portion here and even on this side does have almost like almost a plastic coating on it, if that makes sense. So not gonna have to worry about scratching up your trailer that way, you know, if you get the bare metal it can start causing rust and things like that. And that's probably really important on those galvanized trailers as well. You don't wanna take that coating off and wear them out. So has a few small features that aren't a huge deal but are definitely nice to have. Something I do wanna mention, I actually talked to quite a few of our customers and a lot of them have multiple different trailers. Whether you have a coupler for work and maybe one for play. So gave me an example on just your more traditional style coupler that you would see on a utility trailer, something like that. But let's say on the weekends, you got a camper like this. So you drop your work trailer, pick up the camper and vice versa when the weekend's over. Well, if it we're me I would want a lock that would fit both of them. That way you don't have different locks and different keys. So on a coupler like this here on our camper I tried to put our master lock on there and it's just a little too wide. I feel like I could probably force it on there but it's not ideal. So if that's your case and you want one lock for multiple trailers when you drop them, there is a solution. And that would be an adjustable lock. Something like this here. This is the etrailer one. It's a nice product. And I'll show you how this works. So what you do is unlock, it actually slides off and you can see how much adjustability you're gonna have there. So pretty much any coupler at this point something like this would work for. So this slides in, and then you take your lock and it kinda locks in as far as you want it to, as far as you push it down. So it's gonna give us those same security features but with a little bit of adjustability. So, you know, say if your coupler was even, your coupler latch was super wide. And so say all the way out here. You know you can lock that down right there and cover that full span. So I just wanted to offer a solution for those of you that might have those multiple different trailers with different size coupler latches, and was looking for one easy lock to use, that'll work with pretty much anything. So something else you can actually use these coupler locks for. I know I do personally, whenever I'm towing a trailer is to use it as a latch pan as well. So let's say, you know you hook up to your tow vehicle, you get your ball in there, you lock your latch down. A lot of people would tend to grab just the latch pen like this, right It's got to work fine. It's got to go through and prevent that latch from coming undone, that way you're not gonna disconnect from your vehicle. Well, one of the things you can do is more or less eliminate this and use the coupler lock for it. You get in the habit of doing that. You know that this is not gonna come unlocked when you're going down the road. And it's gonna get you peace of mind knowing you're a little more secure. And then you just get in that habit and you're not gonna have to throw this in your truck or whatever, when you're using your trailer. That said too whenever this is in place, you know let's say maybe you're going on a trip and getting tired, swing into a hotel overnight to get some shut eye. You gotta know that someone just can't come up, pull off your latch pen, push your trailer off to the side or whatever, hook up to it and burn out with it. So again, just something small, that's gonna work as a great deterrent to keep all those people with bad intentions off of your property. I do know when it comes to trailers some people do tend to store them for quite a while, especially seasonal type trailers like a camper or a boat, wave runner, stuff like that. And one thing you can use in conjunction with a coupler latch lock is a coupler lock like this as well. To just kina give you a little bit extra security if you know it's gonna be set in for awhile. And the way this is gonna work is go around the head of your coupler there, and a pen, this pen here it's gonna get pushed up into it and you're gonna lock it down. And this is gonna be on there. And honestly, really no way to take this off unless you have the key. And it's just going to kinda take that extra step towards making sure that your trailer isn't gonna go anywhere. So at the end of the day a really simple, awesome device here that's gonna make sure everything is secure and help you sleep a little bit better at night. And that'll finish up our look at of the master lock trailer coupler lock..

Customer Satisfaction Score:

Customer Reviews

7/8" Wide Trailer Coupler Latch Lock by Master Lock - 2878DAT

Average Customer Rating:  4.8 out of 5 stars   (47 Customer Reviews)


This is a replacement for the same model that wore too much after 5 years. It works great and fits our coupler (7/8" wide) perfectly.


Pretty self explanatory but it’s a nice lock. You have to use the key to lock it as well as unlock it. Don’t just snap the pin closed thinking you’ve locked it.

Worked great on my harbor freight trailer build.

Feels solid.


I have a 2-5/16 coupling and the latch is 7/8 inch wide. So I went thru 3 locks before I found this one and like it the best.


Fits my trailer coupler latch, adds another layer of protection, and was reasonably priced.


My trailer’s hitch clip tends to bounce loose on dirt roads. Not only does this unit prevent that, but also dissuades would-be trailer thieves. I’m very happy with the lock.



It’s still working well a year later.


ty the time and the item where perfect . Wish had 4 G phone I`m still old school with a flip phone :( I would send pictures , again ty for product. the carpet worked fine as the lock was great. The bow roller fits great. the swivel trailer jack fits great and man what a relief to be able to jack it up with it . I was using car jack to unhitch the boat . Need it badly , TY!!!!!!!!!!!!


Nothing will stop everything, but this with the etrailer coupler lock will make it tougher and maybe they will move on to another trailer. Very satisfied.


This coupler latch lock works great!!! The covered key hole protects the lock from corrosion so this lock should work for many years


Works great to lock trailer while hooked to vehicle.


use when traveling peace of mind, hitch won't come off going down road and trailer will not be stolen while not in vehicle


Works great, nice having key cover to prevent freezing of lock cylinder.



So this can lock the trailer from detaching or attaching to a tow car? do I still the the big thing that blocks the ball receiving part?

Patrick B.


This will secure the latch and prevent it from operating thus helping to secure the trailer both when hooked up to a tow vehicle and when parked. However, when parked, a thief could use an undersized ball that would fit in the coupler without operating the latch. Remember none of the locking systems will be theft proof, you can only seek to make it more difficult to steal and thus discouraging a thief from targeting your trailer. A coupler lock, paired with a wheel lock, will make any trailer more difficult and time consuming to steal.


Nice quality lock. It does have a nice thick plastic outer coating. Protects against scratching your trailer and scratching the lock itself.


My previous coupler locks have been the type that requires turning the key and screw the lock closed. This plunger design is simpler & faster to use.


I like the simplicity and weather resistant design of this latch lock. It seems to me to be at least as secure as a pad lock. Being a Master is a plus.


It feels solid, seems to work well so far, my only complaint is that the key hole is taller than the key is and so its annoying trying to get the key started but I think its something I can get used to with time



Still struggle with getting the key started, but it has held up great, lock still turns easily, the pin slides in and out like when it was new. There is some small spotting of rust on the pin, but nothing overly concerning. The dust cap has held on and still feels solid, not soft and flimsy. I don’t how many of those things I have lost over the years on various hitch accessory contraptions when the tether on them breaks. I would buy it again.


I really like the design of the lock, easy to put on and off. Seems like a good build and should get my money's worth out of it.


just what i needed a lock that you can tether to the trailer tongue so that you do not lose it


What can I say, it’s a Master lock. Well-built smooth operation and it does exactly what it was designed to do!


Just a normal hitch lock works for what I need it for!


Your product works moderately well, although it bent slightly


I use it to secure the latch on a boat trailer. Works exactly as advertised.


Very close fit, well built. Made by Master Lock.


My items came shipped timely as promised, and all met my expectations exactly as I needed!


Excellent lock. Just what I was looking for. It’s well sealed to prevent water from getting in and freezing.


Nice and compact. They have stepped up their game. Product has improved over their past products.

Show More Reviews

See what our Experts say about this Master Lock Trailer Coupler Locks

  • Will Master Lock Coupler Latch Lock 2878DAT Fit a Fulton 2-5/16 Inch Trailer Coupler
    Provided that the hole in the latch on your Fulton coupler is 1/4 inch or larger and the width of the latch is less than 7/8 inches then lock # 2878DAT will fit. It has been my experience that Fulton couplers for 2-5/16 balls do match this description. I have linked a video review of this lock for you.
    view full answer...
  • Pin Width of Masterlock Trailer Coupler Latch Lock # 2878DAT
    Yes, the width of the pin on the 7/8" Wide Trailer Coupler Latch Lock # 2878DAT that you referenced is 1/4 inch.
    view full answer...
  • Dimensions Of Master Lock Trailer Coupler Latch Lock
    I pulled one of the Master Lock Wide trailer Coupler Latch Locks, part # 2878DAT from our warehouse to measure for you. As the enclosed photo shows the inside dimension from the barrel to the lock arm measures 7/8 inches and the depth of the lock is 1-1/4 inches. I have attached a link to a product review video for this lock you can check out.
    view full answer...
    Image 1 for
  • Master Lock That Is Keyed Alike To Match Existing Key
    The 7/8" Wide Trailer Coupler Latch Lock by Master Lock Item # 2878DAT is not a keyed alike lock. You would have to purchase four locks that can be keyed alike. I recommend the Master Lock Shrouded Padlock Item # 37DAT. You can key as many as you want, alike.
    view full answer...
  • Is the Master Lock 2878DAT Able to be Keyed Alike
    Though I do have another option for you, the Master Lock 7/8" Wide Trailer Coupler Latch Lock # 2878DAT is not able to be keyed alike, unfortunately. With that being said, the Trailer Coupler Latch Lock - 7/8" Span - 1/4" Diameter - Stainless Steel # e98890 will be a different design, but can be keyed alike. This is also made in the USA.
    view full answer...
  • What Material is the Trailer Coupler Latch Lock # 2878DAT Made From
    The 7/8" Wide Trailer Coupler Latch Lock # 2878DAT is made of hardened steel. As far as how easy it is to defeat, ultimately any lock can be defeated given enough time and the right tools. Since there is no gauge of how "breakeable" a specific lock is, we recommend making your setup look intimidating to deter would-be thieves. If you are wanting to deter theft of your trailer when it is coupled then the Bulldog # BD580404 is a great option because it has a coupler lock and a ball mount...
    view full answer...
  • Trailer Coupler Latch Lock with a 1/4 Inch Diameter Pin Longer than 3/4 Inches
    We have several latch locks that have longer pins you could use. Master Lock Adjustable Trailer Coupler Lock - Stainless Steel Item # 2847DAT has an adjustable span of 9/16" to 2-3/4". Stainless Steel Trailer Coupler Lock # e98890 has a span of 7/8" as does lock # 2878DAT. I have linked videos of these locks for you.
    view full answer...
  • Trailer Coupler Latch Lock with 1 Inch Pin Span
    Master Lock has an adjustable latch lock, # 2847DAT that has presets for either a 1 inch span or a 2 inch span. We also have some that are 7/8 inch spans which is 1/8 of an inch more than a 3/4. We have # e98890, # 2878DAT, and # e98889. I have linked some video reviews of these locks for you.
    view full answer...
  • Recommended Trailer Coupler Latch Lock Keyed Alike
    I reached out to my contact at Master Lock, and the 7/8" Wide Trailer Coupler Latch Lock # 2878DAT are keyed at random and do not have the ability to be keyed alike. For a similar option you can use our # e98890 which can be keyed alike. Alternatively, you may be interested in the Fastway Universal Trailer Coupler Lock for 1-7/8", 2" and 2-5/16" Couplers # FA86-0015-318 which can also be keyed alike and add even more security. I've attached a video review to assist.
    view full answer...

Do you have a question about this Trailer Coupler Lock?

Info for this part was:

Employee Michael H
Expert Research:
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Employee Joshua S
Video Edited:
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Updated by:
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Employee Ryan G
Installed by:
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