What’s That?: Plastic Cardboard Box Latch


Okay, here’s your next bit of plastic part design geekery: This single polypropylene part is a latch mechanism that holds a corrugated carton closed (like for plasma TVs). It’s passed though a hole that goes through two walls of corrugated (the top and the bottom) and then the two locking surfaces are pushed inward, hooking onto the backside of the inside of the carton. The latch is locked in place with a snap, which can be opened by squeezing…


What? You don’t think this thing is cool? Not convinced, huh? How about a little video demonstration:

Okay, now for a few points of interest: This part takes advantage of polypropylene’s flexibility – particularly for snaps and living hinges. The image below shows the part in the position it’s molded in. Part of the mold comes from underneath and part from the top, but they meet in the middle at a “bypass” to create a break between the two moving parts. Except they leave a little bit of flash to connect them (and probably to improve the flow of the material in the mold). That flash is broken when the latch is used for the first time…


Actually, those hinges should be actuated a few times (maybe a dozen or so) when they first come out of the mold (and are still warm) to get the molecules oriented properly across the thin wall section of the hinge – otherwise the hinge could be brittle and crack if used more than a few times. But my guess is that since these things are only used a handful of times before the carton is tossed (into the recycling bin, of course), they probably don’t go through the trouble of actuating the hinges at the press.


See how the pair of snapping ribs engage the shorter ribs on the other side? They even have an angled lead-in to make snapping easier… Sweet…

Here’s something else to point out about the back side of the part: Dig the texture on the sides… Why would they go to the trouble to add texture to any surface of this part, much less the back surfaces that are crammed in the carton? Because the texture makes the part stick to the back half of the mold when it opens. Once completely open, the part is ejected. If you want more information about gates (particularly how the gate got over to the “B” half of the mold), let me know.


Here’s a few more shots of a slightly smaller version of the same latch, in white, but it shows how the latch fits into the carton:




The funny thing is that I’m sometimes more fascinated by these little gadgets than the thing in the carton… again, much to the amusement of my co-workers…

An engineer I used to know when I first got out of design school told me something I’ll never forget:

Reduce the number of parts to one, and then look at deflection.

What he was saying is that you should look for ways to take full advantage of the material’s natural properties. In this case it’s the flexibility (in the living hinges and in the snap) as well as its durability (this thing won’t break – even in cold temps).

I don’t know who designer is or manufactures this thing, but it’s cool. If you do happen to know who designed this or something like it, let me know…


13 Responses to “What’s That?: Plastic Cardboard Box Latch”

  1. 1 caserrr July 24, 2009 at 4:57 am

    A few years ago, I worked for a temp agency that sent me on short-term jobs, mostly to warehouses/commercial type places. One of them was the moving company that handled local deliveries for the Sony store, and TV’s were pretty much all we moved. I remember being very fascinated with these clips. After some strange looks from my co-workers, I don’t think I ever mentioned them to any of my friends, and I never thought I’d really think about them again, let alone read an article about the very things I found interesting about them. Cheers!

    • 2 Warren Ginn July 24, 2009 at 9:25 am

      I know, I love these little things… I’ve seen a few variations on the theme with different ways they fold up… Can you imagine doing the development on one of these? Like a little origami puzzle… Don’t worry about not mentioning them to any of your friends – they just wouldn’t understand. 🙂 Glad you liked the post.

    • 3 John November 17, 2009 at 6:43 pm

      Can anyone tell me a supplier please?

  2. 5 Liav July 24, 2009 at 10:23 am

    This is a great series. How does a non-industrial designer start learning this sort of stuff on his/her own?


  3. 7 Threed Rixnor July 24, 2009 at 7:17 pm

    How cute. And only 20,000 years for it to decompose in a landfill, as opposed to a few months for the cardboard box. Yeah, yeah, it can be recycled, blah blah blah, but how much do you want to bet it gets tossed with the box? Let’s see a clever way to latch the box using the box itself, not another piece of plastic.

    • 8 Warren Ginn July 25, 2009 at 9:47 pm

      A legitimate concern. My only response here is that, in at least our case, we actually re-use the cartons to transport these large displays to different locations and the plastic clips make re-using the cartons much easier. The alternative would be to have a large, all-plastic crate constructed.

      Thanks for you comments,


  4. 9 Ducktape July 25, 2009 at 9:38 pm

    Oh man, I’m so glad there’s someone else that is fascinated by these, too.

    When I got my HDTV, I found these neat things on the box. I saved them and have them on my coffee table, certain that I could find something to do with them — which so far, has been to play with them, and baffle my visitors who wonder why I have these things on the table and am so fascinated with them.

    Whew! It’s not just me!

  5. 11 jimharris@icpms.com September 12, 2012 at 12:33 pm

    Hello! Yeah, sounds like there are people like me who are sometimes fascinated more with the box, than what’s inside! Like kids on Christmas afternoon. The place that I found these at is: http://www.alenfield.com I found a pen that when you squeeze the back button, the sides release, and fold/swing out of the way for the tip!

    James Blonde

  1. 1 Plastic box-latches are surprisingly cool | timnhanh.us Trackback on July 24, 2009 at 7:05 am
  2. 2 Top Posts « WordPress.com Trackback on July 24, 2009 at 8:21 pm

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