4 pack silicone cowboy hat straw covers cap compatible with stanley cup 30 40 oz. Inspired by cowboy hats, these unique and distinctive straw toppers are compatible with Stanley cup tumblers. Made from food-grade silicone, they are BPA-free and dishwasher safe.  It is nice for most straws with a diameter of 9-10 mm (0.35-0.39 inches). Their unique style makes them a great choice for personal use or as a gift.