One-way ratchet knob

A knob that turns one way with a click per tooth and locks the other, like the dial on a strap or cord tensioner. The base screws to a panel and carries a ring of sawtooth teeth and a centre post; the knob snaps onto the post and its springy pawls ride over the teeth. Choose the size, how many clicks per turn, which way it turns freely and how stiff the pawls are, and tune the two fit numbers for your printer. Both parts print flat with no supports.