See picture above
A conveyor screw is either left hand or right hand depending on the form of the helix. The hand of the screw is easily determined by looking at the end of the screw.
The screw picture on the left has the flight helix wrapped around in an counter-clockwise direction, or to your left same as a left hand thread on a bolt. This is termed a LEFT hand screw
The screw picture on the right has the flight helix wrapped around in an clockwise direction, or to your right same as a right hand thread on a bolt. This is termed a RIGHT hand screw
A conveyor screw viewed from either end will show the same configuration. If the end of the conveyor screw is not readily visible, then by merely imagining that the flighting has been cut, with the cut end exposed, the hand of the screw may be easily determined