Parametric headset spacers for bicycle threadless headsets

**Update 9 Jan 2020:** Thanks to [zachariazh](https://www.thingiverse.com/zachariazh/about) for pointing out that you can pay nearly 20€ for what is basically the [same exact thing](https://www.extralite.com/imagesbike/ExtraBolt/Eb103dp.jpg) from [Extralite](https://www.extralite.com/Products/ExtraBolts_anglo.htm), the Italian manufacturer of super lightweight weight weenie parts. The only thing you don't get with my design is the "Extralite" logo printed on the side. Considering their scale photos compared to mine, I thought about putting an "Extraliter" logo on mine but that might be a bit much.

Plenty of headset spacers here on Thingiverse, probably because a headset spacer is basically a simple hollow cylinder. Not the most complicated design.

What makes mine different? Not a whole bunch, but I do have several varieties available along with the basic simple spacer:

* Hourglass spacer
Thicker at the ends, thinner in the middle. Results in the lightest spacer which is pe