For UPWARD OPENING FLAP DOOR used with concealed , piano or butt hinges. SDS C301N is designed to hold door in closed and opened position. Non handed. Torque Calculation: Torque = Door Height 1/2 Door Weight Per Piece: 40~70 kgcm (35~60 lbsinch) Per Pair: 80~140 kgcm (70~120 lbsinch) Recommended Door Thickness : 20 mm (25/32")