RockSlide Nickel plated brass Guitar Slide large size: 21.5mm x 59mm. Large Rock Slides are one of the heaviest on the scene. This makes for killer sustain on the thickest of string gauges and a down-right dark sound. Nickel plated-brass Rock Slides are a great combination of tone and string feel. They are slippery like glass, but have the weight and long sustain of brass. Unlike the polished brass slides, they remain slippery for a very long time.