NOTE: This block was removed in Refined Storage 1.7. The landscape for covers and multiparts in Minecraft 1.14.4 is a bit unclear, so time will tell if this feature returns, or if Refined Storage will utilise a multipart library if that is available.

A Hollow Cover is the same as a Cover but has a hole so you can pass cables through it.

You can also put it on the front of an Importer or [Exporter] to hide part of the block.

It will let a network signal through.