This is a light switch timer knob that I designed to replace the one that had broken.  It is easier to twist than the OEM version that came with the switch.  Installation involves lining up the flat side in the knob hole to the flat side of the pin on the timer switch and carefully pushing the knob onto the pin.  I printed this in PETG with a 0.4mm nozzle and 2mm perimeters (sides, top, and bottom).  With those settings, infill percentage doesn't really matter.