to clog a small crack in a pipe. Turning off gas range. Putting on, taking off smoke detector. Unscrewing the bulb that's off;
how to work with a window that is stuck and won't close; office chair, drop ceiling, covers on fixtures radiators, etc.
more examples of "מבטל כלי מהיכנו" (nullifying a vessel from its normal usage) that come up on Shabbos;