For UPWARD-OPENING FLAP DOOR used with piano, butt or concealed hinges Opening angle 80, 90 or 100 NSDX-35 is designed to hold door in fully opened position Speed adjustment screw located on front for easy adjustment Two stop version (holds door at 65and 90) is also available Torque Calculation : Torque = Door Height 1/2 Door Weight Per Piece: 20~70 kgcm (19~60 lbsinch), Per Pair: 40~140 kgcm (38~120 lbsinch)