The ESTF-P024-ULC-000 uses duplex LC adapters, so a 24-port tray only uses 6 sets of LC/UPC lifting adapters.  The base E-Series tray can hold up to 12 sets of lifting adapters, so there is more for additional LC/UPC lifting adapters.  P/N ESTF-ULCA is the individual lifting adapter and can be purchased and install on the open slots of the E-Series tray. One must consider the physical limitations of the E-Series tray when adding additional LC lifting adapters to ensure the additional fiber cables still allow for easy movement of the internal cable management components.