I used to know this back when i worked with Flash animation, but I'm working on a 3D printer now and I've forgotten, when you have a set of teeth, on a linear shaft and a gear, do you base the unrolling of the gear, for the spacing, on the inside of the teeth, the outside of the teeth, or the halfway point between the two? Like if i have a shaft with 1x1x1 teeth, of Pi length (like 3.14 inches tall) do I line up the inside of the gear teeth holes, or the outside of the gear teeth, or something in between? I know i have to bevel the teeth in either case to fit. I could have sworn I used the average diameter between the teeth inside and outside, but is that how it works in physical reality? It always looked good in simulations.