Couples

A couple is a pair of equal and opposite forces acting on a body along parallel lines.The moment of a couple = one of the forces × the perpendicular distance between the lines of action of the forces.A couple is a pair of forces that are parallel but act along different lines.
The moment of a couple is known as a torque.
The torque of a couple = one of the forces × perpendicular separation between the forces.
Torque = F d