These patent pending valve caps stop air from passing through, which forces your exhaled air back through the filter of your mask. The unique, innovative design prevents airborne germs and particulates from spreading as you navigate indoor environments. Certain states require this design. With this pack, you'll receive 2 valve caps, which include a cap and a base. They are compatible with every model of RZ Industries' mask. These caps only have to be replaced if you lose a piece or if damage occurs. Stay healthy and go out into the world with confidence using these effective valve caps! 1.5 inch diameter.