Remove the old base and install it.Align the center core base with the center core part,press down to check the snap embedded in the center part hole. The installation is complete. When installing the center core,the air vent hole should be aligned with the filter outlet. Replacement base for 59053800,59053700,59053600,59053500 center core. Center core base replacement for Clean and Clear pool filter. The groove on the center core base fits the protrusion at the bottom of the filter.Please proper alignment when installing.