The rook kit is used as a spacer for a true 5" post. Simply slide the rook over the round pipe and fasten with the included screws. Once installed, just slide the 5" vinyl post over the rook post mount adapters for a professionally installed vinyl post. Each rook kit includes 2 rooks and all the screws necessary for installation. The rook kit comes in 2 sizes based on the size of the existing pipe.