For DOWNWARD-OPENING FLAP DOOR used with piano, butt or drop hinges (SDH-001, SDH-P, P.238 HDS-10 is designed to hold door in closed and opened position Used in pairsTorque Calculation: Torque = Door Height 1/2 Door WeightK-Type (Light Duty): 140~200 kgcm (121~173 lbsinch)/pairM-Type (Medium Duty): 200~250 kgcm (173~216 lbsinch)/pairH-Type (Heavy Duty): 250~300 kgcm (216~260 lbsinch)/pairWARNING: This product can expose you to chemicals including Bisphenol A (BPA), which is known to the State of California to cause birth defects or other reproductive harm. For more information go to www.P65WARNINGs.ca.govWARNING: This product can expose you to chemicals including nickel and chromium, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65WARNINGs.ca.gov.