Answer :
The “auger hole, bored about half an inch or so, into the plank” develops the symbol of Ahab’s whalebone leg by revealing Ahab's commitment to his mission on revenge.
In the lines “auger hole, bored about half an inch or so, into the plank” the speaker is describing the influence Ahab has on him while meeting him for the first time. The passage describes the auger hole on the deck which Ahab uses in order to steady his leg. The passage also describes Ahab’s white whalebone leg and how he build it out of a sperm whale's jaw. The speaker describes Ahab's commitment to his mission by focusing on his strong willpower.