Tightening a screw on Shabbos
Question
Is one allowed to tighten and to loosen screws in an adjustable reading-stand on Shabbos? It has screws with large heads for adjusting its height and angle. Is one allowed to adjust its height by loosening and then tightening the screws? Is one allowed to loosen and tighten the screw that controls the angle of the reading surface on top? (When the screw is loose, it’s impossible to put a book on it, since it will just fall off.)
Answer
It is permitted to loosen and to tighten screws of the reading-stand, both the ones that control its height and the ones that control the angle of the reading surface. The reason is that this is the way this reading-stand is always used – by constantly adjusting its height.