My bathtub has a little plunger that toggles between water coming out of the faucet or the shower head. The knob at the end of the plunger broke off and left the threads inside the plunger. I could have drilled it out or something else similarly drastic but instead I designed a better shaped knob which I pressed on and epoxied on. It was a smooth rod so I went with the "we'll do it live" method.