Features Extended Using --- Had the lase head been equipped with an O ring, it can use 12mm, 16mm and 18mm lenses for more convenient work. Applicable Lens --- Support D12 FL50.8, D16 FL25.4, D18 FL50.8mm focusing lens, and can install a mirror with a diameter of 20mm. The Working Tips --- 5 x 8 silicon flexible tube is recommended, the lens adapter is inside the laser head, please search carefully. Perfect Match --- Made of aluminum alloy material with blue oxide coating, the laser head with air assist suits for K40 laser engraver. Easy to Install --- Comes with a light weight and a compact size as well, the installation is very convenient to completed in minutes. Specification: Item Type: Laser Head Material: Aluminum Alloy Applicable Focusing Lens Diameter and Focal Length: Approx. 12 ~ 50.8mm / 0.47 ~ 2in, 14 ~ 25.4mm / 0.55 ~ 1in, 18 ~ 50.8mm / 0.71 ~ 2in.  Package List:1 x Laser Head Package List 1 x Laser Head