The standard in look, feel and functionality. Unlike any ring before it. Inner Grooves allow air in and moisture out with a comfort radius to give you maximum breathability and performance. Specs Perfect Design with unique medical-grade materials for undeniable quality beyond any silicone ring that came before. In a class of its own. SM designed for wrist sizes 160mm - 200mm LG designed for wrist sizes 180mm - 220mm Anodized aluminum clasp clasp button Sport style clasp Premium medical grade silicone 316 stainless steel integrated interface Compatible with series 1-6 Apple watch