<p>This is a laser head with air-assisted .</p> <p> With the O-ring in the lens holder, the laser head now can install a 15mm diameter focus lens too. </p><p> The mount is capable of hosting a 20 or 18 or 15 or 12mm diameter focus lens and a 20mm diameter reflection mirror. </p> <p> Focus lens and mirrors are NOT included</p> <p>Air plug outer diameter: 5.5mm. </p> <p>This is a great replacement for K40 or D40 that comes with no air-assisted in original packing</p> <p>NOTE: the Lightobject engraving air assist can be attached to this laser head</p>