This Vertical Pipe comes in a 24" size that will fit both the Universal Kayak Adapter and Power Pole Adapter.
Size is measured from the very top of the adapter to the very bottom.
As reference, the following adapters ship with the following sizes:
*Power Pole vertical pipes are shipped with a set screw in place and locked. To enable steering, you will need to remove set screws. All other Vertical pipes ship "open".