18350 and RCR123A

I just got a laser that calls for 2 x 18350 3.7v batteries. I don't happen to have any of these on hand but I do have a few RCR123A that say 3.7v. My question is are these interchangeable with 18350? They are both 3.7v which is what I thought was the most important thing(correct me if I'm wrong, I don't know anything about batteries).
Also I was under the impression that 2 x 18350 were the same as 1 x 18650. I thought that stacked on top of each other 2 x 18350 were the same length as 1 x 18650 and the same diameter, however when I put a 18650 in my new laser it was too tight a fit so this threw off my theory(again correct me if Im wrong, I really dont know anything about these batteries).

Any way, I hope this was all comprehensible, and thanks for reading. Id love some advice.

Thanks