Roommate was struggling with a jug of tea. As caps get lower and lower in profile, there's a lot less to grip, and trickier to open. Put the M3D to work with its awesome Tough Ink (orange heft, specifically, and with minimal infill, though you could get away with thick and hollow walls). The larger one was built around a gallon jug of Lipton tea (which is almost the same size as an Ocean Spray bottle's cap). The smaller one was built around a bottle of Source Perrier (a fairly typical 2-liter bottle cap size). Between these two, you should be able to cover most plastic bottles with screw-on caps. If it's a little bigger or a little smaller, just turn the horseshoe around and use the long ends like tongs to get a grip.