I would ask him. It has a picture of a empty three element lens barrel. The two element barrel is a little shorter than the three element for obvious reasons. I pair the two element with green diodes and the three element for blue with blue diodes.
The two element lenses that I know of are actually fairly widely coated but are slightly less pass with no difference in beam shape compared to the three element for blue ones on blue diodes. The two element gives a small bump for the 520nm diodes compared to using the three element for blue with 520nm diodes as I used to pair the three element for blue with the 520 diodes till I found the two element. Both lenses are supposed to be coated 400-600nm for blue/green diodes. I just pair them with diodes based on the best peak and both produce the same spot size with either lens but both can be used with either.
I did ask him. But his reply left a lot to be desired. He said it was between the g2 and the 3 element. Embelish a little lol. J thanks for explaining. I have been messing with different lenses with a ex BE trying to get a square output.