Any rigid body transformation can be expressed as a screw rotation about and translation along an axis. The screw is usually defined by a line (a unit direction and point on the line), a displacement, and an angle. The pitch is the ratio of displacement to angle and indicates handedness.
It seems straight-forward that if a line with opposite direction is used, both the angle and displacement change sign. Therefore, two screws would be identical if they have opposite direction, displacement, and angle (maintaining the same pitch). Is there a convention or constraint that rectifies these identical screws (such as maintaining an always-positive displacement or angle)?