A plumb line; a cord to the end of which was fastened a metal, stone, or clay weight that kept the line straight and made it possible to build walls and other structures that were straight and perpendicular to the horizon. The weight itself is sometimes called the plumb  bob, or plummet. Carpenters, masons, and other craftsmen of ancient times used the plummet.

In connection with the rebuilding of the temple in Jerusalem, Zerubbabel is represented as having in hand a plummet, literally, “the stone [or, weight], the tin,” according to the Masoretic text. (Zec 4:9, 10) As foretold, not only was the temple’s foundation laid by Zerubbabel but under his supervision the work was carried to completion.​—Ezr 3:8-10; 6:14, 15.

In vision, Amos beheld Jehovah stationed on a wall made with a plummet, and thus one that was originally straight, perpendicular. Jehovah was seen holding a plummet, and the prophet was told that God was setting a plummet in the midst of His people. As Israel did not meet the test of straightness in a spiritual way, not acting in accord with God’s requirements, Jehovah would mete out justice and “no more do any further excusing of it.” Israel’s high places would be laid desolate, her sanctuaries would be devastated, and God would “rise up against the house of Jeroboam with a sword.” (Am 7:7-9) True to these words, Israel was devastated and Samaria destroyed by the Assyrians in 740 B.C.E.