A valve cap is the plastic cap that screws over a valve; usually, valve caps are used on a car or bicycle tire. Because a valve cap has nothing to do with actually sealing the air inside a tire, many wonder why companies use them. Despite what most assume, valve caps do serve a purpose depending upon the valve. Valve caps for style points. We're pretty sure that whoever said valve caps weren't cool had never seen the Deity Components Presta Valve Caps. These sleek little aluminum caps protect your delicate presta valves on the ride, while boosting your style wtih seven different color options to coordinate with your trusty steed. Bicycle inner tubes usually come with plastic valve caps. These keep the valve clean, and that is all. A Presta valve cap will work on a Woods Valve, but a Woods valve cap is too short for a Presta valve.