One piece 21" (20-4-720A-611-1) block and tackle side load window balance 21 Block and Tackle Balance for Non Tilting Windows Stamp number: 20-4 / Channel Depth: 5/8" / Channel length: 21" Top Guide Number: 720A Bottom Guide Number: 611 Terminal Clip Type: Knotless Weight Capacity(lbs.): 17-22