Wanted a grommet/passthrough with a little more resistance so it also acts as a cable stop. For added “cable-stopping”, put a zip tie on the inside. I made these primarily for lightboxes, but they will work on anything really.

The hole is 18mm, one lip of the grommet is smaller than the other side so it goes in pretty easy, but is a tight fit when in snapped in. If you need more flex in the hole, cut it out a little more with a razor.