Ultimate Knob Generator with Metric and SAE presets

thingiverse

This is a remix of wstein's [Ultimate knob generator](https://www.thingiverse.com/thing:713300) but with presets for Metric M1.6 though M36 and SAE #8-80 though 1"-8. I was also inspired by https://www.thingiverse.com/thing:5532943 but wanted handles for some SAE/imperial nuts. It also cleans up a few deprecated OpenSCAD warnings. Shown is a 1/4"-20 nut knob threaded onto a carriage bolt. A set of STLs for the simple knobs in Metric M1.6-M12 and SAW#0-80 - 1"-8 are included, along with M6 and 1/4-20 knobs in the hex, rounded, cylindrical, clamp, and wing forms are included. It works in OpenSCAD version(2021.1.0) and now in the thingiverse customizer's OpenSACD 2015.3.0 version, which is difficult to debug. I discovered that per https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Customizer#Drop_down_box the options can't be quoted for Thingiverse. OpenSCAD treats ```// ["M2", "M3"``` like ```// [M2, M3, ...``` but thingiverse's customizer chokes on it.