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The SENSE M2488C computer monitor pictured here has 4 machine screw holes at standard spacing around the label on the back of the monitor.

I plan to mount it from a ceiling mount, not on my desk.

I have a ceiling mount bracket with holes of exactly the same spacing. But the screws that came with the ceiling mount bracket are too large in diameter. Meanwhile, the screws that came with the monitor that connect the desk foot to the monitor are too small in diameter.

I can look by eye at the ceiling mount holes and I see that they are threaded for a machine screw of a certain length, diameter, and thread pitch. I cannot afford to try the wrong screws because then I would ruin these built-in holes.

What is the correct way to measure the hole, particularly diameter and thread pitch, so that I can just go to the hardware store and purchase exactly the right machine screws?

Catalog photo of the back of the SENSE M2488C monitor

  • Basically, unless you have a sample screw to start with, you have to determine the screw diameter and thread pitch by trial and error. If the test screw doesn't fit, don't force it. – Hot Licks May 30 '17 at 2:52
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My experience with monitor/tv mounts is that they're usually metric. If that holds, you should be able to measure the hole, round to the nearest integer millimeter and order those machine screws. (M4, M5, M6, etc.)

Try and screw them in by hand first. If you've got the wrong size, you'll get resistance. (In other words, you won't strip out the sleeve if you're not forcing anything.)

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    Worked. "By hand" is the key phrase. I even found that the right screw seemed to stop fitting for a moment in one of the holes, but then realized that I simply must have been putting in it not quite straight. Patience setting it in just right and it worked again. Bracket well-attached to monitor! Now I just have to find the right screws for the part that's on the ceiling-mounted pole. But now I know what to do. – talkaboutquality May 29 '17 at 17:23
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    "By hand". Definitely. For completeness, if the screw location is restricted so that you cannot get fingers on the screw head to twiddle it, you may use a screwdriver (magnetized usually best!) ... but only to twiddle the shank between your fingers, not to twist the handle with your hand. – nigel222 May 31 '17 at 8:28
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You already discovered the answer for your monitor. I'll leave a general answer for others with a similar question.

The Video Electronics Standards Association has a set of standards for mounting flat panel displays like TVs and computer monitors. It is usually referred to as simply the VESA Mounting Standard. Pretty much any modern display that has built-in mounting holes complies with this standard.

The standard defines a hole pattern (usually rectangular, but larger sizes can have more than four holes and there can be a center hole), and screw specification (the screws are metric). The best explanation I found of the details (outside of the actual standards), is this Wikipedia article: https://en.wikipedia.org/wiki/Flat_Display_Mounting_Interface

The hole pattern and screw specification are based on the display's size and weight. If you see a rectangular hole pattern and the measurement is consistent with the standard for a display of the size and weight of yours, it's a safe bet that its a VESA mount. A quick summary of mount dimensions to check against:

VESA dimensions summary

(Click on image for more readable size) courtesy http://www.ergotron.com/en-us/support/vesa-standard

A more detailed table, including screw specifications, from Wikipedia:

VESA table

Notes:

  • If a screen is heavier or larger than specified in table 1, it should use a larger variant from the table, for instance a 30-in LCD TV weighing more than 50 lb (23 kg) would need to use a part F mount.
  • The weight limits were unusually chosen as round numbers in kg or lb for different sizes.
  • The screw lengths for part C, D and E become whole numbers when adding a 2.6 mm thick bracket (which is how the standard describes them).
  • The screw lengths for part F are minimum / maximum / hole maximum, as in: M6 screws must go at least 9mm in but at most 10mm in, and the hole might not be deeper than 12mm.

    The minimum length is important for strength. The maximum length is also important. You don't want the screw to force its way into the inside or to bottom out in the threaded insert so that it can't be properly tightened. Some mounts come with screws that are longer than necessary and then use spacers behind the mount to correct the effective length. If you use one of those screws as a guide at the hardware store, make sure you have any needed spacers.

There is additional detail, especially for larger sizes, in the Wikipedia article.

The VESA mount screws are likely to be different from those used to attach a stand for desktop or tabletop use. Note that, particularly for larger displays, the display manufacturer is allowed to choose screws different from the standard. If they do, they must provide the screws with the display, in which case you need to use the display manufacturer's screws in lieu of those supplied by the mount manufacturer and should have a sample.

If the display came with screws and you no longer have them, you might find a reference to their size in the product documentation or might be able to find the information online (or check with the manufacturer's customer support). Otherwise, it's trial and error for the thread (for an initial estimate, you can compare the hole diameter of the threaded insert to a chart of screw dimensions). I would refer to the VESA spec for the screw length, and verify that the threaded hole accommodates that length.

  • This. You should be able to find some VESA mounting screws easily. A quick search on Amazon yielded some potential winners(although they're pricey). – Machavity May 30 '17 at 12:46
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    @Machavity If you search by the screw size itself "M4x12mm" you can find somewhat cheaper options and have plenty of spares for when you drop one and can't find where it rolled to. (eg several sources offering 50packs for $7.50, or a 20pack with hex head tops for $4 if you can accept slower 3rd party shipping.) – Dan Neely May 30 '17 at 13:49
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    Or if you are in Germany, you can walk into your local hardware shop and buy half a dozen M4x12mm for cents. – Martin Bonner May 30 '17 at 14:17
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    Unfortunately manufacturers seem to be in the habit of using the VESA mounting patterns but ignoring the screw size part of the spec. – Peter Green May 30 '17 at 16:00
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First look in the manuals for the mount and the monitor. The bolts for the monitor matter more than the mount since the mount holes are larger so the bolts will be stronger than needed. If the monitor bolts will fit cleanly through the mount holes, just use them with whatever washers are appropriate. M8,M6, M4 bolts are common, the size can be measured with a caliper, the major diameter (OD) is how they're sized. There are only a few common thread pitches; finding bolt matches is easy. Just be sure the bolt insertion length is sufficient and tighten the bolts well. The bolts won't break but if they're not inserted far enough, they can easily be stripped, so get longer ones if needed.

There is a good design factor in VESA mounts. For a given pattern, monitors or TV panels with a large range of weights can be found. Yours is not heavy, I wouldn't be too concerned if the bolts are long enough.

Recently, I made a pedestal mount for a 75 lb plasma TV from a tilting wall mount, a base and rectangular tubing for the uprights. Got tired of the crummy built in speakers. I had similar concerns as yours but the final product is rock solid even with another 15 lbs of speakers outboard of the TV. The whole thing is held by 4 M8 x 1.25 bolts, tilts fine, slides easily and doesn't totter at all; far more stable than the original pedestal mount.

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Just to add to what fixer1234 said, I wanted to note this specifically (emphasis mine)

I have a ceiling mount bracket with holes of exactly the same spacing. But the screws that came with the ceiling mount bracket are too large in diameter.

It sounds like you bought a TV mount (these are common in most electronics stores). While flat screen TVs are essentially giant monitors nowadays, monitors are much smaller and lighter than their TV counterparts, despite sharing the same mounting standards. In the future, I would try to find a mount specific to monitors. They can easily be found online and will almost certainly have screws to fit your monitor.

Meanwhile, the screws that came with the monitor that connect the desk foot to the monitor are too small in diameter.

The screws to attach the included stand to the monitor are almost always non-standard and rarely designed for mounting. I have a 60" TV at work and it has some tiny screws in the stand that do nothing more than keep it from falling off when you pick it up.

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First, are the four screws around the label made for mounting the unit? Most screws are just to hold covers on, and have no strength behind them. If the manual doesn't say "do it", don't do it.

Second, the way you match screw threads is take one out and haul it to the hardware store. Real hardware store, not Home Depot/Lowes/Menards, those places are building supply stores.

  • Thanks. Once I knew what I was looking for (Mx metric screws) I was able to go to that department in our office and find them! – talkaboutquality May 29 '17 at 17:20
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    It is a fairly safe assumption that four screw holes on the back of a monitor arranged in a rectangular pattern are designed for interfacing with a VESA mount. I would be hard-pressed to find a flat panel build in the past 15 years where this is not true. – user4302 May 29 '17 at 23:25

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