Here's what rockslide have to say:
Clear Glass Rock Slides are individually hand moulded in the USA by master lampworkers. These have all the same features as our brass Rock Slides® with the Knuckle Cut, Finger Rest and Tapered Interior. These fit almost exactly like their brass counterpart but are slightly longer. The main difference being that they are much lighter & faster so you can really cook with these on an electric guitar. Because of our unique tapered interior design they do have enough mass to light up your acoustic.
Colored Glass Rock Slides patterns are hand blown so they vary from slide to slide.
Small The small Rock Slide is the sports car of the bottleneck world and fits comfortably on the pinky finger. The tapered interior helps it stay on by itself so you don't have to focus on bending your finger in the slide to prevent it from moving around or falling off. This gives the index, middle and ring finger freedom to play.
- I.D. at Opening: U.S. 11/16" or 17.5mm
- Weight: 1.3oz or 36g
- U.S. Measurements: Cutaway side, 1 9/16 "
- Overall length, 1 7/8 "
- Metric Measurements: Cutaway side, 40.5mm
- Overall length, 47.8mm