For UPWARD-OPENING FLAP DOOR used with concealed hinges Used in pairs HDSN-30 is designed to hold door in closed and opened position Arm bracket for wood and aluminum frame avail-able. Specify when ordering Torque Calculation: Torque = Door Height 1/2 Door Weight, In case of opening angle 90 K-Type (Light Duty): 140~179 kgcm (122~155 lbsinch)/pair, M-Type (Medium Duty): 180~219 kgcm (156~190 lbsinch)/pair, H-Type (Heavy Duty): 220~259 kgcm (191~225 lbsinch)/pair, S-Type (Super Heavy Duty): 260~300 kgcm (226~260 lbsinch)/pairWARNING: This product can expose you to acrylonitrile, butadiene, styrene, 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.