Unistrut Heavy Duty Fiberglass Channel Nuts are made from glass reinforced polyurethane. They're designed to be used where high thread shear values or spring nuts are required. Thread Shear Limit: 1,400 lbs. Torque Limits: 3/8" and 1/2" = 8 ft/lbs. 5/8" and 3/4" = 10 ft/lbs. NOTE: Heavy Duty Fiberglass Channel Nuts cannot be used with Lighty Duty 1000 Series Channel or Stainless Steel Series Channel.