MRP AMG Chain Retention Systems. the All-mountain Guide features MRP's patented integrated skid protection and shares the freshly updated upper guide from the G3, but lacks a lower retention mechanism. The All-mountain Guide is a great choice for 5-6" travel bikes when used with the latest tensioned rear derailleurs or on its own for shorter-travel trail bikes or hardtails that require bash protection. The contact-free, "upper-only" chain retention means the All-mountain Guide will be virtually silent and completely drag-free when pedaling. The patented integrated skid will protect your crank and chainring and prevent the chain from ever contacting and potentially damaging your expensive frame.