I bought these for my car but they are marked for bikes... Works the same I think except the length is shorter than the car valve stem cap. The gasket looks well sealed and the quality is good so I'd say overall it's a good buy.
Pros
Robust, reinforced plastic: The WEIDEBACH air cap is made of reinforced plastic to give your nipples the best possible protection against wind and weather. Snow, mud and wind can backfire - they will withstand hardships!