Chain EK 520 HD-QX 120L The DEX incorporates the Quadra X-Ring design which increases chain life from 1.5 to 2 times longer than a standard O-Ring chain. The QX-Ring design also reduces friction by 40% compared to the standard O-Ring chain. Utilizing CRH pin treatment which provides an extremely hard outside coating and softer inside to increase strength and reduce chain wear. Exclusive to EK Chains, theChormiumCarbide pin surface coating also offers superior impact and shock absorption while reducing oxidation caused by natural elements.