Just my lens from AP
But how do connect it to the laser there is a tube with a lens in the end and it comes with a nozzle
???
Generally Focal length is referred to in inches, lens and mirror diameters are referred to in mm. For example, I use a 12mm diameter 4 inch focal length lens. 12 mm dia required precise alignment but 4 inch focal length gives great tolerance in cutting depth.
Seems very illogical to measure a diameter in mm, but a focal length in inches?
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I think most of the world, including American and British scientists usually use metricā¦ for good reason.
In the end, the length is the same no matter the unit, as long as you know the unit.
All of my lenses focal lengths have mm listedā¦ especially the fiber lenses. All of them come from metric countriesā¦ probably has something to do with itā¦
Just one more opinion 
Im so confused in inches and mm lol
Pick one and use itā¦ I do everything in mmā¦ 1/25.4 = 1mmā¦
Even my construction tapes have metricā¦ Itās so much easier to add, divide or multiple or subtract simple whole numbersā¦ compared to doing just simple math such as from 1/16" added to 9/64"ā¦?
Lightburn does itās internals in mm, I understand. In the end it really doesnāt matterā¦ whatever works best for youā¦