I use these Wilson Candy Making squeeze bottles for a lot of things around the shop (this one is for paint thinner), but the caps always seem to get lost or damaged -- and even when they're not lost or damaged, they're tiny and tapered, so they're not very easy to remove. So I made a replacement cap to solve both those problems.

The ridges in the printed plastic hold the cap on tightly.

1. Print. (Tweak the OpenSCAD settings, if necessary, for a good fit.)
2. Apply.

TOOL CHAIN AND PRINT SETTINGS: For this I used slic3r 0.9.7, Marlin, and j-head 0.5mm with cheap 3mm "repraper" PLA filament (from China). I print onto glass covered with window tint with a thin coat of ABS juice. The printbed is heated to 90 for the first layer (measures about 80 with the IR thermometer), and 75 for additional layers. I used two perimeters, 10% honeycomb infill, and 0.4mm layer height. Hot end temperature depends on color, but is usually around 185.