What is the meaning of the plumb?

The plumb—or plumb-rule—serves as an emblem of moral rectitude, integrity, and uprightness of conduct 12. As one of the working tools of the Fellow Craft degree, it draws a direct parallel from the operative builder, who uses a weighted perpendicular line to erect plumb walls, to the speculative Mason, who is expected to maintain an unwavering commitment to truth and justice, bending neither to adversity nor temptation 1. An article on the Grand Lodge of India's website similarly notes that the symbolic principle of the plumb-rule creates exactness of thought, word, and action, reinforcing the general rule that Freemasons are expected to act on the Plumb.

The plumb also serves as an official jewel worn by the Junior Warden, hanging as a badge of his station 21. In this role, W. Finch notes that the implement symbolizes the upright conduct required in governing the lodge and examining strange visitors to safeguard the order 2.

In American jurisdictions, the symbol carries an explicit scriptural reference drawn from the Book of Amos, where the Lord sets a plumb line in the midst of his people 13. Carl Claudy takes this passage to teach how a Fellow Craft ought to judge human effort—evaluating work by a standard "in the midst" of a man's actual circumstances and tools rather than applying an unyielding, distant judgment 3. William Preston further defined its symbolic scope as teaching the criterion of rectitude, the avoidance of dissimulation in word and action, and the directing of one's steps toward immortality, a concept traditionally associated with the rising perpendicular 1.