A Flare Nut is a specialized brass fastener used to secure the copper line sets to the indoor and outdoor units of a mini-split. It works by compressing the flared end of a copper pipe against a fitting to create a high-pressure, leak-proof seal without the need for brazing or soldering. When installing a 2-Zone 18,000 BTU R410A system, using the correct torque on these nuts is critical to preventing refrigerant leaks. We provide heavy-duty brass nuts within our Accessories collection to ensure a professional-grade connection. Because R410A and R454B operate at high pressures, the integrity of the flare nut connection is paramount for system longevity. Over-tightening can crack the nut, while under-tightening can lead to gradual gas loss over several months. Most of our Armbridge Pre-Flared Installation Kits include these nuts for a streamlined setup. It is a fundamental component for any Ductless AC installation project.