I needed a 28mm spline wrench for my milling machine. So, I decided to make one from PLA so that it would break if I forgot to remove it from the drawbar splines.

I printed this as a test with just 15% infill and it was pretty strong. If this breaks, I would probably set the fill to 25-40%.

My machine is pretty well calibrated and this printed for a real snug fit. If your machine is not that well calibrated, I would suggest setting the X-Y Hole compensation values to values that give correct hole sizing on your printer.