US Patent 7661729 Apparatus for connecting plastic-lined metallic pipes

A connector used for connecting the plastic metallic pipe includes a body, a cap, and three washers. The body has a section of thread in its outer wall for coupling with the cap which has a section thread in its inner wall. In operation, first insert the pipe into the cap, then insert the rubber washer, the metallic washer, and spring washer into the body, and then screw the cap into the body, such that the pipe is locked with the body.