Neje A40640 40w laser air assist nozzle

The nozzle is 12mm high, because to cut the max width of material (8mm ply), the focus has to be 3mm above the bottom of the sheet, and that 17mm below the red shield, which is 3mm below the module's bottom. 

So there's 15mm between sheet and module, and 3mm remainging should be enough clearance, or 8mm when cutting 3mm sheets.

The air pressure is not just building up inside and goes wherever there's less pressure but directed outside. 

There's separation between the laser path and the air path inside.

Make sure to set the focus BEFORE installing, as you won't be able to turn the focusing ring once it's on. 

According to NEJE the focus should be 20mm below the aluminium heatsink (they say below the red shield by 17mm)

(Orginal file from Thingiverse imaasz )