Amos, Chapter 7

                                               Verse 7:  "Thus he shewed me: and, behold, the
                                                                               LORD
                                                      stood upon a wall made by a plumbline,
                                                              with a plumbline in his hand.

                                      erse 8:  And the LORD said unto me, Amos, what seest thou?
                                                                 And I said, A plumbline.
                                                                   Then said the LORD,
                                                             Behold, I will set a plumbline
                                                            in the midst of my people Israel:
                                                       I will not again pass by them any more."

This Masonic degree verse,... then, as now, denotes the LORD's plumbline which represents uprightness of conduct throughout one's life. 
The Fellow Craft degree denotes middle age.