The CAT Pumps 20464 is a V-packing spacer backup-ring for pumps. It is used to replace a spacer backup ring inside pumps. Made with PTFE. Backup ring is compatible with pump models 3520, 3520C, 3527, 3531D.44101, 3535.44101, 3521DHS.4410, 3521C.44101, 6821, and 6821K. A genuine OEM part. Ensures a proper fit and material compatibility when installed in the recommended pump models.