These Sur-Seal adapters are KF-25 to 3/4 (0.75 in.) ID PVC Hose and make maximum vacuum tight connections to PVC vacuum hose. The flange size follows ISO-KF standards and is NW-25. They are commonly used to make connections between ISO-KF fittings and PVC Wire Reinforced Hose. The ISO-KF flanges are often called quick flange fittings because they are quick to assemble. The standard sizes for quick flange fittings are KF-10, KF-16, KF-25, KF-40, and KF-50 with flange sizes NW-10, NW-16, NW-25, NW-40, and NW-50, respectively. They are made of stainless steel.