In 1999, The Rock Slide invented the first ergonomic slide which has been favored by professional acoustic and electric players ever since. The signature is a tapered interior design, which fits like a glove. Other features include the knuckle cutaway for finger flexibility and the dished finger rest for perfect control and vibrato. Medium Rock Slides are a perfect weight for most styles, heavy enough for long sustain on acoustic guitars, but light enough to easily control for fast electric playing. 19.5mm I.D. 57.5mm long 70g. USA Ring size 8-10.The Rock Slide Item No. TRS-MBShop like the pros at Sam Ash Music, where discerning musicians go for premium guitar accessories.