The K020B0021-1 is a replacement belt drive (5mm-PITCH, 10mm-WIDE) that is for use with various screw drive garage door openers.
Product Information:
New Part Number: K020B0021-1.
Old Part Numbers: 020B0021‑1, 20B21‑1.
Compatible with Chamberlain, LiftMaster, Craftsman openers.
Use your owner's manual to match the part number.