Do you know, or have you tried using the M30 extension tube on the m20 sized lights and does the light still work?
Well, the diameter and threading is the same, so you can certainly screw the M30 extension tube on the M20/M21 (at least my samples, which are all from early production runs - things may have changed since then). But I have not tried activating the lights, since I am not sure what battery source would fit such a setup (maybe 2x18500?). The circuits for the M20/M21 are voltage limited, so 3x cells would likely blow the circuits. Frankly, there's little advantage to 2x18500 over 1x18650 (especially with newer high capacity 18650 cells), so there's really no point in doing this.
