A simple yo-yo.
With PLA, the correct weight for the yo-yo will be obtained with an infill density of about 85%. Assemble either traditional or butterfly style by pressing the pieces onto a length of 1/4" diameter wooden dowel - wood is really the best material for a fixed axle and will allow the yo-yo to sleep easily. The dowel should be about 1 3/8" long. Happy yo-ing!