Tricky Screw Heads Have Disappearing Slots

Klein Hidden Bolt and Tool

Perhaps you’ve seen them, demonstrations of a machined piece of metal that upon further inspection is actually two pieces machined so perfectly that they appear as one. With extremely tight tolerances, it’s not possible to determine where one piece of metal ends and another begins — that is, until the secret is revealed. Inspired by such pieces of art, [Andrew Klein] sought to put this high level of machine work to practical use. And so it was that his as-yet-unnamed Screw With No Slot came to be.

Klein Hidden Bolt depressed by brass rod
A brass rod pushes down to reveal the keyed center section.

The screw’s disc-like appearance looks as if it’s a metal trim piece to cover a bolt hole. But in the video below [Andrew] shows us the trick, pushing a brass rod into the middle of the disc to reveal the hidden three-point slot. The center of the disk is actually a separate bit of finely machined metal that is spring loaded to stay flush. A specially designed wrench keys into the rounded concave triangle shape cut into the face.

The wrench is made with brass to avoid marring the precision surface. It uses three magnets to hold tight to the screw’s 410 magnetic stainless steel. [Andrew] didn’t spill the beans on how this was done, but we haven’t seen any process other than electrical discharge machining (EDM) that can achieve this level of mating precision. If that topic is new to you, we recommend checking out [Ben Krasnow’s] lab experiments on the topic.

We can’t help but be taken in by the beauty of the fastener, and it immediately sent our imaginations into a National Treasure induced dream-like state. [Andrew Klein] has yet to name this fastener, and he’s soliciting ideas for names in the video below the break. If you have such an idea, you can comment on his video. He’s also exploring the viability of the as-yet-named fastener as a commercial product for high end furniture builders.

This is not the first time we’ve featured [Andrew Klein]’s work. His previous featured projects include a custom sawblade for perfectly foldable joints and an unveiling of the magnetic magic behind switchable permanent magnets. Be sure to submit the neat hacks, builds, and inspiring projects that you come across to our Tip Line!

50 thoughts on “Tricky Screw Heads Have Disappearing Slots

      1. Please no. I am tired of the over use of Sigma, alpha, omega, beta in product names. Mostly because of fools who think dogs and people have alphas males, beta males, and now for some reason sigma males.

  1. This could be a nice finish for some high end equipment where you want to hide all the bolts.

    “It uses three magnets to hold tight to the screw’s 410 magnetic stainless steel”
    I get constantly into discussion with marine engineers that using magnet to determine if the steel is stainless or not is not really reliable. Some of them defend that method despite having magnet bar in the kitchen holding stainless steel knives. Also when I show them my Victorinox atracted by magnet they claim it’s not stainless steel and reject any article about ferritic and austenic stainless steel.

    1. Nickel is magnetic, and often useful in marine environments. It is strange for a marine engineer not to know a lot about magnetic stainless, even accidentally, because they’d need to know about the properties of the nickel anyway.

      Are you sure these are “marine engineers” and not technicians in a job that was named too far in the past to differentiate?

    2. Well, that’s just dumb and obstinate to ignore facts placed in front of you, but it is a good way to test stainless in a pinch. So many things that claim to be “stainless” aren’t. They rust and you wonder what you spent so much money on. If something is claiming to be stainless, and I’m trying to decide if I want to spend money on it, and I don’t have some way of knowing absolutely if they’re telling the truth or not, I’m going to use a magnet. More often than not, if it sticks, it rusts.

    3. There’s only a few grades of stainless that’ll stand up to a marine (salt water) environment for extended time, AISI316 being the predominant one, which isn’t magnetic. So if they are MARINE engineers, I can very much understand them using a magnet as a basic “is this a useable grade of stainless” test for their purposes. Is it 100% infallible, no, but it probably works well enough.

  2. As designed no, but I can see uses where it would be worth the money — as a key to a hidden compartment. That said backing out the screw all the way is not realistic, but having some (preferably mechanical device) behind several of them to make a combination would be interesting and useful. After rethinking it, as long as the the spring loaded bit in the back moves in a way that it can release a catch, I could see using a couple of them. I like the fact it is stainless.

  3. its neat but i cant think of any engineering reason why you would need such a screw beside obfuscation. for purely cosmetic purposes there is for sure more than one way to achieve the same look without using such screws.

      1. Using a metal cap over your screw. You can cut a cylinder into little slugs. If you really want, thread the rod before you turn it into slugs.

        There are plenty of other examples of you read the comments on YouTube.

  4. Hmm, if it can be revealed just by pushing it’s not as hidden as it could be. An improvement could be to make use of the brushed finish to disguise a disk cover. The disk then can be lifted with a magnet, exposing a dowel that can be grabbed with a purpose made wrench to turn the screw. Or just maybe come off altogether leaving behind a simple screw.

    1. Does say its all the same grade of stainless, so it shouldn’t really corrode in general use. Get gummed up and jammed for any number of other reasons probably though…

      At least its a push in to get to screw head model, if you are supposed to pull the turning surface out with a magnet or something and it starts binding up you are in a spot of bother, but push in all you need is a nice bit of soft something and a mallet to smack it with, will probably see it free, at least enough to use once…

  5. Houdini Screw [or Whodeeni Screw].
    Just because we may not visualize an application for this screw does not mean that there is not a pent up demand for it in some specialty market.

  6. You missed a process then Ryan, EDM is perhaps the only automatable way to create such tight tollerance fits with this design, but people have done the same sort of thing by hand with lots of filing and polishing steps before..

    Also can’t see why a ‘normal’ CNC mill of sufficient quality can’t either – you are only interested in super super precision in one plane, so with the right tool in the spindle and a precise enough machine you can get that I would think, might take a few tries to get the fit just right, but its not impossible I would suggest. If you look at how precise the CNC (and manual for that matter) mills used by watchmakers can be in the x-y plane I think you’d find you can make it happen well enough for the effect to work visually quite easily really. Your more coarse big boy mill for industrial and automotive scale engineering might not be able to, its a level of precision beyond their needs, that supporting that precision level would just slow down the normal workflow, but that doesn’t mean the same style of tool can’t do the job in the hands of somebody who knows how to use it…

    1. The precision needed to make this form seamless is standard to any decent mill. It just takes a good go/no go gauge to make this something that can be repeatedly and quickly made to check for the geometric fit quickly needed to nest but not be seen.

      Tolerances of 0.0004″ or so on all of that device would be low enough not to be seen as a seam, but not so low as to cost extreme amounts of money to produce. There are ways to make this seamless with much sloppier tolerances too, like shallow tapers to form- that you lock together, until they bottom out and then you mill them flat.

      The real problem with using something like this is the finer your fit- the exponentially more likely the smallest ingress of contaminants ruin and sieze the mechanism from working, especially from springing back to be flush completely and not really visible.

      To get this finished so seamless there has to be a way of bracing the telescoping piece in place to run a finishing pass with an abrasive finishing belt across the face, without the pc depressing, so the thief brushed finish is completely seamless from the center outward.

      I have had things like this in mind for years with different implementation but I never thought people would be willing to pay the obscene amount of money I would charge.

      1. I can’t speak to any decent mill – as I don’t have any decent mill, only a really cheap chinesium mini mill, that I don’t think could get that precision, even with a real master operator (which I am not). Still a great little tool when you don’t have space for a good more commonly sized mill, but I wish it was better built, and stiffer, the only surprisingly good thing about it is the spindle power, which seems like it would not be out of place on a much much bigger machine…

        I’d also think the degree of round curvy edges to this design would make it difficult to get that perfect on a normal mill – you can certainly do a less rounded design on an mill (even mine) relatively easily, but doing all the curves round the patterns centre would be more challenging – so many centre points for your rotation that need to be really precisely centred for the fit to work out.

  7. Beautifully done. Another route for driving a smooth-top screw is to super glue on a slotted cap. The cap can be removed by a sharp blow or a little heat. Glue a cap back on to remove screw. Not as mechanically elegant, but a lot easier to make.

    1. Or a precision machined smooth cap that’s held on by magnets, and a companion tool that’s used to pull the magnetic cap off.
      I feel like it would be WAY more cost effective than the original design, however cool it is.

  8. In the past there have been things like the spring-loaded flush-fitting foot step recesses in the fuselages of WWII fighters.

    Before asking for a new name, do a good trawl through Google Patents to see if anyone’s done this before, and if so, use that. If no prior art then why not something like ‘fastener with spring-loaded decorative fascia panel’ as that pretty much is what it is.

    This is a beautifully engineered item but realistically I think the production cost would turn out be somewhat more than that suggested.

    1. That would cost too much and possibly make the device repairable once discovered…glue is cheap and if they use enough of the right kind, the device will be unserviceable, which is their holy grail.

  9. Maybe this can have a use in mounting hardware such as hinges and locks to glass doors. But for this to really shine some good use case has to be found.
    Maybe integrate them in anti-theft car wheel covers?

    I also wonder why the key (= one part) is more expensive then the screw. (at least3 parts, including the spring).
    The key can be ceapified by using a standard square socket or hexagonal base material for use with a socket wrench.

    1. when pricing out machinework, you have to think of Actions, Fixtures or Processes, not Components. A single cut pass or planar pass of multiple cuts is a single Process. center spot-drilling then full-drilling a ring of holes using a dividing plate is one Fixture, then 4 Actions per hole (index, drill, swap, drill).

  10. In what situations is this more desirable than covering a traditional screw with a metal plate?

    They already sell similar metal plates with magnets. Removing them can be difficult or easy. They sell coverplates designed to be removed with magnets, or locking tabs so they’re permanent, coverplates that only release when turned, etc.

    Also, in most situations (as in the shown examples) the rear of the screw is hidden. Carriage bolts were created for these situations.

  11. “[Andrew] didn’t spill the beans on how this was done, but we haven’t seen any process other than electrical discharge machining (EDM) that can achieve this level of mating precision.” – Am I missing something? He very clearly states that it’s made with wire EDM.

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