This is the design I like the best for refills after trying many others. Thanks!

Printed perfect and it works great.

I printed using .16 optimal on the A1. And for the worm gear and cap only, I followed @Spikes11's instructions in the comments for setting the variable layer height. The worm gear and cap went together very easy. The rest of the threads were snug, but went together great after a few tighten/loosen cycles. Didn't have to use any tools, but it did take some initial effort. Excellent model, in my opinion.