by whowhatwhere, published
Basically this is heavy duty version of the desk grommet (see http://www.thingiverse.com/thing:2411 ) designed to be used in a workbench.
Rather than just sitting on top of the hole with a lip, this grommet countersinks into the hole and could be glued or screwed in place (3mm screw holes provided).
The "cap" is modeled on a heavy manhole cover 2 parts with a small hole in the center (big enough for a cable or two - but also to get your finger in to help move the cap).
The idea was for a way to drop cables through the workbench but at the same time be able to close the hold with something solid enough to stand things on.
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This design is untested
2 STLs 1 for the grommet, 1 for the lid (2 parts)
Print out, fits into an 80mm hole.
SKP file included for those interested in making derivatives.