This is a dock hinge that mounts to a pipe driven into the ground on land. This bracket should be very low to the ground for stability. Connect the first portion of your floating dock to these brackets.
To avoid confusion when buying pipe that fits in this, the industry standard calls the pipe size as 1.5″ schedule 40 but the O.D. is actually 1 7/8″.
Here is the bracket shown in use below.