This is a really nicely made 3U vent panel. Flat steel with rolled edge at the top and bottom, this leaves about 129mm of space on the back allowing you enough space to mount 120mm fans if needed. The hex hole layout doesn't quite line up for a standard computer 120mm fan, but it's close enough to bodge.
Really can't fault this item if you want to seal up a rack from unwanted fingers, but still want it ventilated.