Air assist input, with 2 outputs the first to blow out the middle to clear off the smoke from the lens, the second directed on focal point from sideway.the bottom part slide on the lens holder, that allow to set the distance between the lens to the object (50mm) depending on object thickness.ATTENTION ! plastic is flamable, do not use without air assit to keep the flame away. enventually make/wrap it into foil shield.discuss the K40 laser cutter with the community : https://forum.makerforums.info/c/k40/26