Heavy Duty Industrial 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. Trolley has threaded rod that extends below the roller track. Pull Rope Trolleys, recommended for curtains over eight feet tall. These trolleys are the strongest rollers we offer. Recommended for applications of extreme curtain weight or height. Thread dimensions 0.375 inch at 16 TPI.