Candle mold, square. Two parts with dimples so the alignment is gooood. One hole at the bottom for filling the molten wax, one small hole at the top to feed the wick. Simply apply a rubber band around the mold and it sticks together snugly.

I poured the molten reclaimed wax from old stumps in the mold while it was submerged in a small bucket to prevent leakage and to help it cool down. After it was hardened the mold popped right off, no fuss. Carefull to pour the wax not to fast, you could trap air in the process (see picture). The finish is rustic, but you could give the candle a small heat treatment (oven, fire, hairblower) to get a smooth(er) finish.

You can resize in your slicer to fit your needs.

PLA works, PETG or ABS works even better (less temp warping), 20% infill quality; draft works just as great but recommend 0.2mm or better.

Have fun burning square candles!