Another Parametric Spool

Needed this for a particular sized spool but figured I would make it parametric. Was quite an easy project actually. Essentially the same as the spool by "caru" (didn't see that). I do plan to make some additions such as a semi-transparent dome top to put LEDs and a cover for the outside of the solenoid. I FINALLY have access (sort of) to a 3D printer but alas it's not functioning right now...figures. It's a replicator 2 and I guess it's under warranty which is why they haven't just turned it over to me to fix! Still trying to convince my own boss to get us one - she needs convincing for some reason... I guess "limitless potential" just doesn't cut it.

It would be nice if the two pieces screwed together (or clipped together) but I'm not sure how to do a screw with OpenSCAD. The extrude and twist is just too unpredictable. I'll be looking into it when I have time, since the printer isn't working anyway I'm not rushing it. Any suggestions would be appreciated. For example how do you replicate a 1/4-20 with accuracy?

The actual use for this is to demonstrate how waves (water) can make energy. There is a bobber - like a toilet bobber - that bounces up and down giving about an inch to an inch and a half range of motion and I'm just trying to get enough voltage to power an LED but haven't been successful thus far. Couldn't find a spool with the right diameter so why not just print one! With a zener diode and capacitor we got it to work but the speed needed just won't cut it with the previous coils I made. So this will be take 2 (or 3). If it doesn't work at least I made the effort to make it adjustable. If I can't get the juice I need I'll have to go rotary. Again, any suggestions are welcomed and appreciated.