Model Rocket Guide Ring for cutting tubes

This is just a simple ring to go around a model rocket body tube. Estes sells a kit like this, but that'd be expensive for a classroom, so if you need a dozen guides for cutting BT-50 tubes this might be better.

WARNING: I only tested the BT-50 fit (I couldn't find another body tube in the house)
WARNING 2: My printer may need a different "FUDGE" factor than yours. If it's too tight or loose, open the scad and change the fudge.

I was also thinking it'd be "easy" to make adapter rings to nest body tubes. Included in the scad is a function that has the different ID & OD sizes of the body tubes, so it'd be "easy" to pick an OD for one tube and an ID for another tube...

This is NOT used in my full size Lego R2-D2, http://L3-G0.blogspot.com - he doesn't have the rocket jets