NIBCO PC604 3 PRESS x M ADAPTER.NIBCO press fittings are the fastest, easiest way to join copper tubing systems. NIBCO Press System fittings are designed to join with seamless copper water tube in residential and commercial potable, hot, chilled and process water applications for plumbing and HVAC systems. The press fittings can also be installed underground. The NIBCO Press System is user friendly, quick and easy to install. When properly crimped a unique “N” witness mark is clearly visible.