A locking mechanism (10) for a hinge (4) is disclosed. A latch member (11) engages with a lip (12). A positive drive means (20, 23, 24, 41) enables the latch member to be driven into and out of engagement with the lip. The driven engagement when the hinge is used in relation to columns (1, 101) prevents small movements at the hinge being magnified into large movements at the end of the column members. The driven dis-engagement enables the hinge to be opened notwithstanding mechanical loads, corrosion, insect nests and similar obstacles. The drive means preferably takes two forms, namely threaded fasteners (20, 23, 24) and a spring loaded rotatable actuator (41) with ramped surfaces (48, 49) which male with ramped surfaces (61, 62) on the latch member (11).