The water shut off valve knobs for toilets and sinks break, get lost and rust away. The replacement knobs from the hardware store often do not fit the valve, or will not slip over the ridges on the valve shaft due to previous damage from pliers, vice-grips - unwieldy in tight work spaces - and the like used to turn the valve in the absence of the handle. A universal knob with a threaded hole, perpendicular to the valve shaft, in the female socket of the valve would accommodates a threaded, pointed Allen screw. The tightened Allen screw holds the handle in place.-- Sunstone, Feb 04 2013 Water shut off valves and handles http://www.lowescre..._p_web.jpg?sfvrsn=0 [Sunstone, Feb 04 2013] Pointed Allen screws https://encrypted-t...8c5O-QykxzHRjuCKYZAPointed allen screws used to bind the water shut off handle to the shaft [Sunstone, Feb 04 2013] Allen screws bind a mandrel to a shaft http://www.ganoksin...art/BL-Lathe-31.jpgThe Allen screw tapped into the female portion shut off valve handle would bind the handle to the shaft in the same manner [Sunstone, Feb 04 2013] //pointed Allen screw//
This is known as a “set screw”.-- ytk, Feb 04 2013 I've seen a trend to a 7mm square tap spindle / shaft recently. Seems to be gaining popularity.-- UnaBubba, Feb 06 2013 random, halfbakery