Wurkkos offers “shorty tubes” for many of their lights that convert 18650 body light to a 18350 light? In general, can 16340 fit in these 18650 shorty tube lights?
I looked up the specs on these two battery types and they seem to be similar (i.e. max 4.2V, LVP should be ~3.0V). I might have to be careful about charge currents since the original 18650 built-in hosts may charge the smaller batteries too fast. Any other concerns?
some variables to be aware of
some lights require button top, some require flat top, so whichever type works for 18350, should be the same type chosen for 16340
another variable is length, some button tops tend to be longer than most flat top batteries
example of a mismatch:
you may not be able to use a protected button top 16340, in a light that works with an unprotected flat top 18350, because the protected button top is 3mm longer, and may prevent the light from closing all the way, preventing the body tube from making contact with the driver
the main difference is the 16mm diameter battery will fit more loosely in the 18mm inner diameter body tube… making it easier to cause the battery to rattle… this is solvable with a bit of paper or tape around the battery… it is more of an issue with lights that have a brass button instead of a spring, for the positive contact on the driver…