I still have a Pila GL3 sitting around with a Lumens Factory drop-in. I don't use it much because of the peculiar battery requirement -- 3xCR123A in series. I do not recall what were the original Pila cells that worked in this. I know there's one that is a direct match to a CR123A, but have a vague feeling that there was one about 1.5 times the size, so 2 of those cells would work in a GL3. Is that right?
EDIT: Yes, 18500 cells. They're 50mm in length, just about 1.5 times a CR123A. Found
an old post of mine from 2013 where I had discovered the Pila 300P is equivalent to an 18500.
Anyway, I've always loved the look and feel of these Pila flashlights. "Built like a tank" is absolutely true. I've got a used excellent condition GL4 on the way. This takes 2x18650 so I'm now looking at a Sportac drop-in to use with it.