Two forces F and -F having the same magnitude, parallel lines of action, and opposite sense are said to form a couple.
Moment of the couple,
The moment vector of the couple is independent of the choice of the origin of the coordinate axes, i.e., it is a free vector that can be applied at any point with the same effect.
Two couples will have equal moments if
the two couples lie in parallel planes, and
the two couples have the same sense or the tendency to cause rotation in the same direction.
