Check the listing for details. RJ-12 or RJ-11 Telephone Round Panel Mount Adapter Plug. Condition: New. Listed at 11.95 USD. If you need to add a panel-mount connection for telephone-interfacing projects but don't have the time or ability to cut a custom oval or square hole, this RJ-12 or RJ-11 Telephone Round Panel Mount Plug is the easiest and fastest way to panel-ify your existing phone kit. It's about 30mm in diameter so that you can drill a hole in your wood, plastic or metal with a common hole-saw or bit, no special shapes or filing required. Unscrew the plastic nut, insert the plug, and re-attach. Ta-da: Now you have a pass-through RJ-12 jack. Note that RJ-11 and RJ-12 use the same connector! The difference is that RJ-11 has only 4 wires inserted, while RJ-12 has all 6. So you can use this adapter for either. Note that this is not compatible with RJ-45 Ethernet Jacks or plugs; those are bigger and have more contacts. It's designed to easily attach to a panel up to 16mm thick (or 0.625") or as thin as a few mm. Perfect for adding a port to your project enclosure! We particularly like this adapter for its solid body and 'forgiving' plastic lip that hides the drill hole.