Choose Dunlop Pyrex Glass Slides for a warmer, thicker tone accentuating the middle harmonics of your sound. Processed from high quality boron silicate. Heat treated and annealed to produce a flawless tube. Medium fits ring size 11. Medium with heavy wall fits ring size 10-1/2. Large fits ring size 14.Accentuates the middle harmonics of your sound Processed from high-quality boron silicate Heat treated and annealed Medium fits ring size 11 Medium with heavy wall fits ring size 10-1/2 Large fits ring size 14