The Oxford Valve Caps are made from lightweight CNC machined anodized alloy with a internal 'O' ring for a perfect air tight seal.Lightweight CNC machined anodised alloyInternal 'O' ring for perfect sealFinishing touch with airtight sealIt 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.PLEASE NOTE: Image for illustration purposes only. Sold as a pair.