EK-HTC Classic 12 (Hard Tubing Compression) Fittings are 12mm hard-tube compression fittings designed for use with solid tubing such as Acrylic and PETG. With a high-quality finish, the EK-HTC Classic Fittings are an aesthetically appealing and secure option for your custom loop liquid cooling system. A non-intrusive, minimalistic look, with NO added branding at all. The locking ring prevents solid tube to be pulled out of the fitting by compressing the rubber gasket underneath the ring. EK-HTC Classic fittings are available in the three most popular color options such as nickel, black and black nickel. The barb and the ring are made of CNC machined brass and the seal is made quality rubber O-rings. The base fitting surface is smooth and has no adequate gripping surface, but the inside of the bard is socketed with a 9mm hex Allen key pattern. It's highly recommended to use an Allen Key 9mm (purchased separately) to prevent skin damage to the fingertips while installing the fitting. Please, be advised not to use excessive force when attaching fitting barbs using Allen Key 9mm in order to prevent damage to other liquid cooling products! These fittings have guaranteed compatible with all other EK Water Blocks liquid cooling products. Technical data: - Thread: G1/4" BSP; 4.5mm male thread length - Supported tube: 12mm OD - Outer diameter of a fitting: 19mm - Installed height: 12mm - Compatible solid tubing: Acrylic, PETG, Copper, Brass, Stainless Steel