Heavy Duty Industrial Overlapping Curtain Trolley with Four Steel Wheels. The double steel wheels on steel bodies are recommended for curtains weighing more than 100 pounds or over 15 feet tall. These rollers are compatible with the 16RT tracks. Use the overlapping trolley to provide 11 inch extension of curtain panel without the interruption of wheels. Designed to prevent gap between two curtains. Especially useful over doors, clean rooms, and rooms that are heated or cooled. Includes two 1 inch hooks extending below track.