This nozzle does not just drop in to the KW40 Chinese laser cutter.

Lasers
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1

This nozzle does not just drop in to the KW40 Chinese laser cutter. You need a completely different mirror/lens holder and different lens to use this item. I am not complaining, I am just letting folks know. I couldn’t find any information on this offered nozzle so I bought one to see if it would work. I was hoping the the only thing I might need to do it make a lens holder. But the threads on the nozzle don’t fit anything on the K40 and the lens needed for this to work is quite a bit larger.
http://www.ebay.com/itm/10600nm-CO2-Laser-Cutter-Engraver-Head-Air-Nozzle-Dia20mm-lens-FL1-5-2-2-5-3-4-/331209909829

2

Myah, it’s why I choose 3D print my own to press fit over the bottom retaining ring (the ring you unscrew to get to the lens). Much better.

3

I bought a 3d-printed air-assist that also has a holder for a red-dot sight :

http://www.ebay.co.uk/itm/Air-assist-nozzle-kit-for-K40-40W-CO2-Laser-cutting-engraving-machine-/151517519998?var=&hash=item234725e07e:m:m1lmlgUg1szKb5ugIwEtTlQ

4

Ebay UK has quite a few bits and pieces for the K40, i assume that Ebay US does too.