I would avoid using hdmi couplers for gang plates and keystones in a home theater. For an office it’s fine but if you’re playing back hdcp protected content you can run into issues with these things. More on reddit.com

I have used female to female keystones a lot. It makes it easier to move cables around behind the panel to line up with your equipment. Just be sure to label where the cable is going to - I would use a variation of - labeled on each port (see https://linuxweenie.blogspot.com/2020/06/tips-1-patch-panels-and-markings.html for some ideas). More on reddit.com

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A lot of metal machining involves flood cooland / mist that is partly water and partly oils. I wouldnt be surprised that some of those oils would attack the plastic and cause it to eventually desintegrate. Given the industry, I think explosion-proof housings wouldbe an overkill... but installing they keystone jack in an "outdoor electical box with cover" / "weatherproof box covers" (the clear cover tends to be polycarbonate which usually is a lot more resitant to chemicals). The boxes tend to have rubber rings and grommets so that the cables can enter while keeping most of the moisture out. Its probably the cheapest option. Look for "in-use cover kit" (as the covers are deep enough to allow you to plug the ethernet cable and still close without putting too much stress on the cable). Something like "TayMac MKG420CS Complete In-Use Cover Kit" (ideally a die-cast version) - something like this https://www.grainger.com/product/TAYMAC-While-In-Use-Weatherproof-38R685 More on reddit.com