PCL Air Technology CO17A13 Twin Chuck (Straight & Angled) - There are two types of connector. It is therefore important when purchasing connectors to specify whether a closed or open end type is required. A Closed End connector is used when air is supplied directly from a an air line (i.e. compressor or air receiver). A non-return valve unseats on connection to the tire's valve allowing air to flow into the tire. An Open End connector has a pin which unseats the tire's valve when is use. For use with inflators and cannot be used on the end of an air line.