Hi,
Over the years, whenever I installed and wired in a metal gang outlet or switch box in my house, I always just twisted the green wire grounds together, and then securely grounded them to the metal box itself by simply twisting around a pan-head screw (with a flat washer) thru the metal box right into the wooden stud.
Have now seen some articles and posts where this is not the right way to do it, but they never say why not, or what is the right code approved, way.
Would appreciate any comments and thoughts on.
Thanks, B.