@sickmanfraud This is correct. I have my screens made to specs that created best performance with my kit pieces.
Usually all glass pieces differ slightly from each other as they're blown and handmade. You can press and deform the screens to make it fit in almost every 14mm/18mm stem. It's pretty easy.
Pinch in this manner and the screen will widen slightly. Repeat in small amounts till the screen fits your piece.
are people cleaning the inside of the whip (if it even gets dirty) and how?
Not sure what material your whip is comprised of, but...
With the tubing I provide with my kits (high temp food grade silicone), I always suggest pressing out with a rolling pin... watch as anything inside comes out the end like toothpaste out of the tube!
Then an ISO Soak to completely clean out.