eK-Torque STC 10/16 Black fittings are eK's new minimalistic 10/16mm (ID/OD) soft-tube compression fittings designed for use with various flexible soft tubing types such as PVC, ePDM, Norprene and silicone They can be complemented by interchangeable aesthetic color rings, and are an ideal choice for anyone and a perfect match with eK-Quantum series products (aesthetic rings are sold separately) The locking ring prevents solid tube to be pulled out of the fitting by compressing the rubber gasket underneath the ring The base fitting surface is smooth and has no adequate gripping surface, but the inside of the barb is socketed with a 9mm hex Allen key pattern The outer diameter of a fitting: 23mm