The heavy duty brass compression fittings are used in our stainless steel misting applications. They are dual ferrule fittings designed to compress on hard tubing and hold without leaking. These fittings are compatible and rated for our 1000psi misting systems. Our heavy duty brass compression fittings are compatible with nylon, copper, and stainless tubing. It requires 2 wrenches to secure the brass compression ferrule to the tubing. Please pressure test the tubing when you are finished to check for leaks. If there is a leaky fitting, add a little more torque to the fitting for security and that will stop the leak. **Hint: the ferrules are loose inside the fitting; make sure not to take the nut off. Loosen the nut then push the tubing into the fitting until you feel it hit the center of the fitting. Tighten sufficiently to compress the ferrule onto the tubing.