Made these for a friend who works at a hair salon. I had to use green glass thick acrylic. The Proofgrade ones broke. Feel free to adjust the width and length of the inner slot.
I wonder if Delrin would be a better material? If you try it out let me know.
Cool idea and design… Thanks for sharing 
Oh, how cute! Thanks!
Is that the same as Delrin (or acetal)? If so, I’ll bet it would work. I made some inserts for my dishwasher flatware basket out of it several years ago to cover the bottoms that had been damaged by putting stuff in there sharp side down, and they are showing no signs of damage or warping.
These are so cute!
Way cool design for the key! 
I made these for rolling up thin stuff as getting the inside to stay tight is quite difficult, and then pulling the twister out keeps the material in a tight roll.
@bill.m.davis Having just rolled up the mylar covering for double-sided tape that insists on sprawling all over. 8 feet or so of it would make a great clock spring, just enough force and long time working due to how thin it is.
Really? That is very interesting. I never suspected mylar could be used. But do you have any idea how much torque it generates? That is my biggest problem right now, not getting enough consistent torque to keep the clock running.
It would be very consistent. Different thicknesses would have different torque. What I was using was 2" wide and was difficult enough that it made me think of it like a clock spring. if you put the key in the middle of the length you balance the force and double the torque. The distance would be the ratio of the outer diameter to the inner (rolled up) diameter times the circumference of the inner diameter.
A combination of math and experiment could tell more but worth a look.