user43025: Arduino sells a holder for the UNO board, but without much documentation or detailed specifications, see this link.  Can anyone give the diameter of four small holes, two located on the top edge and one each on the left/right edges?   What size of screw will fit?  They are smaller than M3 / 4-40 apparently.
Also, does anyone know what material is the holder made from?


user33680: Arduino UNO holes are just over 3mm in diameter. Both 4-40 and M3 bolts will work well, giving you a bit of wiggle room. You will have to file down the width of the bolt head to fit against the 6 pin header near D13.
As far as the holder material, I don't know. I 3D print my own.

user43025: ** Self answer:
I obtained several of these holders from Arduino starter kits.  They are made from a clear, colorless plastic that seems to have been injection molded.  However, it is hard to tell exactly which plastic, since these does not have any recycle logo!  The image posted in the original question is perhaps a newer version.  
The four smaller holes can accept M2.5 screws, I checked.

43025: <p>Arduino sells a holder for the UNO board, but without much documentation or detailed specifications, see <a href="https://store.arduino.cc/holder-type-uno" rel="nofollow noreferrer">this link</a>.  Can anyone give the diameter of four small holes, two located on the top edge and one each on the left/right edges?   What size of screw will fit?  They are smaller than M3 / 4-40 apparently.</p>

<p>Also, does anyone know what material is the holder made from?</p>

<p><a href="https://i.stack.imgur.com/FOuTZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FOuTZ.png" alt="enter image description here"></a></p>
 33680: <p>Arduino UNO holes are just over 3mm in diameter. Both 4-40 and M3 bolts will work well, giving you a bit of wiggle room. You will have to file down the width of the bolt head to fit against the 6 pin header near D13.</p>

<p>As far as the holder material, I don't know. I 3D print my own.</p>
 43025: <p>** Self answer:</p>

<p>I obtained several of these holders from Arduino starter kits.  They are made from a clear, colorless plastic that seems to have been injection molded.  However, it is hard to tell exactly which plastic, since these does not have any recycle logo!  The image posted in the original question is perhaps a newer version.  </p>

<p>The four smaller holes can accept M2.5 screws, I checked.</p>
