Ek hdc fitting is a solid tube compression fitting designed for use with solid tubing such as acrylic copper stainless steel or any other type of compatible hard tube ek hdc fitting is a more secure variant of the ek hd adapter fitting as it prevents solid tube to be pulled out of the fitting by compressing the rubber gasket underneath the ring the barb is made of nickel plated cnc machined brass while the ring is made of black anodized cnc machined aluminum and feature quality o rings these fit