Dunlop Tempered Glass Slides offer a warmer, thicker tone accentuating the middle harmonics of your sound. Processed from high quality boron silicate. Heat treated and annealed for a flawless tube.
Durable, seamless glass for a crisp, bright tone.
Model 218 specs:
Usually made from Pyrex, can also be tempered glass
Slides typically are sized S, M, L, and XL, which refers to the inside diameter, specifically.
These are approximate — slides vary from model to model and are handmade. The basic process is to figure out which finger you want to use, get a ring size, figure out what material/type of slide you want, and get close. It doesn’t need to fit like a ring. A little space is a good thing: snug enough to stay in place and have control but loose enough to be comfortable
Shorter slides are useful if you want to wear a slide and switch back and forth between fretting and sliding. A shorter slide allows your finger to bend and tuck out of the way.
Longer slides can cover across the entire neck (all six strings) allowing more immediate note choices and possibilities.