Designed for use with box rail to mount sliding door project, if you are building a heavy sliding door, this will helps.
4PCS Heavy Duty Trolley Wheels
-Product Name: 4 Wheel Trolley Assembly
-Material: Steel, Galvanized Zinc, rust protection
-Max Load rating: 440pound/200kg
-Strut rail size(inside diameter): 2 1/4" H. x 1 3/4 " W or Taller
-Screw Diameter: M12 (0.47inch/12mm)
-Screw Length: 4.7inch (120 mm)
-Fixed mode: welding positioning or Bolt positioning