I want to install an RO in a 2” thick countertop. How can I extend it so I can fasten it from underneath? There is ¾” poly underneath it.?
Use a large dia hole cutter to counterbore the plywood and only fit through the quartz.
Use a female pipe threaded coupling and male nipple made of stainless or brass. Home Depot or Lowes should be able to get you what you need. I'm assuming you mean Reverse Osmosis when you say RO. The stems on the bottom of fixtures are straight pipe thread not tapered so ask the plumbing associate or go to a contractors supply store and get what you need from them.