The Jim Dunlop 215 Thick Glass Bottle Neck Slide. Today's most popular slide for lightining fast licks. Choose the Jim Dunlop 215 Pyrex Glass Slide for a warmer, thicker tone accentuating the middle harmonics of your sound. Today's most popular slide. Processed from high quality Boron Silicate. Heat treated and annealed to produce a flawless tube.