The lens is the final component that the laser beam will pass until it hits the surface of the workpiece. This lens has a focal length of 50.80mm or 2 inches. The diameter of the lens is 20mm. Make sure to get/make the correct nozzle that has a 20mm seat for the lens.

A 20mm lens and final mirror needs to be mounted in this part. The lens mounts in the tapered (conical) section of this part. Notice the component showing partly blue. This is the air assist tube inlet fitting.