Called the "greatest innovation in mini painting history" by Metalhead Minis, the Paint Preserver is a life-saving ring for your paint bottles! This package includes multiple sizes to fit most major paint brands.
The 'Citadel' size has an inner diameter of 32.5mm. This fits Citadel's wider-than-everyone-else Pots.
The 'Monument' size has an inner diameter of 30.5mm - this holds Monument, Cuttlefish and Miniataire paint bottles, to name a few.
The 'P3' size has an inner diameter of 30mm - this is a slightly more snug version of the Monument size for a tighter fit on P3 pots.
The 'Dropper' size has an inner diameter of 25mm - this holds Reaper, Vallejo, GSW, and other common dropper bottle sizes.
Due to minor differences resulting from printer calibration, over-exposure, etc, as well as manufacturing tolerances with paint bottles themselves, you'll generally want to test-print a single holder, and then scale up or down 1-2% at a time to dial it in if needed.