The Bike-It Piston Shape Valve Caps allow you to add some individuality to your bike - however, they are not all about looks.Unique Piston shape cap with Aluminium constructionPrimary method of ensuring a good seal at Tyre ValveAdd some individuality to your bikeProtect Valve Seal from dust, dirt, moisture and road saltIt is widely believed that the cap on a tyre valve is mainly a dust cap. It is certainly important to protect the delicate components of the tyre valve from the effects of dust, dirt, moisture and road salt, however the tyre manufacturers will say quite clearly that the cap is the PRIMARY method of ensuring an air tight seal at the tyre valve.Although the core is part of the sealing mechanism, complete pressure security can only be achieved by means of a good fitting with a proper rubber seal.