Measure the length between each stake pocket to be sure they are the right fit for your bed rails. Measure each stake pocket individually. The hole in your bed rail should be only as big as the stake pocket and no larger.
Measure the center of each stake pocket on the bed rail and mark it with chalk. Mark the size of the whole stake pocket around the center with chalk.
Use the drill to pierce a hole on the place you marked on the bed rail. Enlarge the hole with the drill until it’s the size of the stake pocket.