Knob Studio makes replacement knobs — star, fluted, wing, T-bar, or knurled — around an ordinary metal hex nut, so the threads stay steel while the grip is printed to fit your hand. Pick the fastener size first: the hex pocket is cut so the nut taps in with light interference and can never spin. Head Diameter is the feel parameter — bigger means more torque with less effort. If your printer's pockets run tight or loose, Fit Adjust trims the fit without touching anything else. Knobs print face-down with zero supports, so the visible top face comes out glassy straight off the bed. Tap the nut home with a vise or a gentle hammer blow; no glue needed.