Water rocket fins (can be printed on a 20x20 printer)

thingiverse

It's the concept of USWaterRockets adapted for standard 20x20cm printers. Four fins remain in the corners, making it easy to print without issues. To adjust it to your rocket's diameter, measure the bottle's diameter and add the width of the 3D print edge - usually 0.4mm on each side. Apply that percentage to the model scale in your slicer. For example, my bottle measures 90mm; I add 0.8mm from the edges. I leave it at 91mm to avoid a tight fit. To print, I scale the part to 91% in vase mode. It's essential to print in vase mode.