This design was inspired by the BNTO by Cuppow [ http://www.cuppow.com/collections/bnto-jar-lunchbox-adaptors ]. Unfortunately, Cuppow only makes BNTO's that fit wide-mouth jars. Since we only have narrow-mouth jars, I grabbed a few dimensions with some calipers and CAD'ed up a narrow-mouth version. DISCLAIMER: I make no guarantees that this part is food-safe. The toxicity of 3D printed parts is under debate and is not well understood. This is a proof of concept and is not intended to actually contain food. I assume no risk or liability for your use of this part. USE AT YOUR OWN RISK. Thanks!1) Rotate the part 180° so the open end is facing down. 2) Print I printed this part using a Printrbot Simple 1405 and I did not use any supports. I printed the part upside down (open end facing down) because I worried about the cantilevered lip not printing well without supports (its a substantial overhang). I haven't tried it in any other orientation, or with supports, so I can only recommend printing it upside down with no supports. The inside bottom of the cup will be a little "stringy" with this method.