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I was browsing this website and noticed that they have drilled washers.

enter image description here

I could start to guess that the purpose of drilled washers may involve reducing weight by removing material (although this would compromise its structural integrity and ability to do its job as a washer of distributing a bolt’s load) or maybe the holes allow for greater grip/frictional force somehow.

Maybe it is used when a huge bolt is to be surrounded by a circle of bolts that would fasten the washer. But at this point, it does not seem reasonable to call it a washer anymore?

Steven Lu
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    I've seen similar items designed to increase mechanical engagement when held on by adhesive – Jonathan R Swift Sep 12 '21 at 11:21
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    Looking at a few websites, their main function seems to be to look pretty in applications which are not very critical and easily visible. Motor bike customization seems a popular use for them. Compared with everything else, the weight saving is negligible. – alephzero Sep 12 '21 at 13:09
  • Re my first comment: https://catalog.pemnet.com/viewitems/varimount--base-plates/stainless-steel-varimount--base-plate – Jonathan R Swift Sep 12 '21 at 14:07
  • Yes, re: J Swift's comment, I've seen flanges with this kind of shape, in studs and hardpoints meant to be embedded in fiberglass/epoxy structure.. Alshough some of them, like the third one, don't look like it because the holes are too small. Could it just be a combination washer for a bolt pattern, to reduce part count? – Pete W Sep 12 '21 at 15:21
  • FWIW, upon closer inspection, the diagram that is labeled M6 has the ring of holes in positions that are not even placed symmetrically (unlike the other illustrations), so to me it does call into question the relative sizing of the holes for that one too. – Steven Lu Sep 12 '21 at 23:41

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Depending on the size and thickness these could be spacers. One example is their use on cars to increase the track.

They can also be designed as flexible drive plates between a motor and gearbox for example, with alternate bolts for the motor.

Some are also designed as seals or separation plates between things like pipe flanges.

Solar Mike
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