Securing the Pivot

I was checking the lower metal handrail for the night transit route when a faint ticking caught my ear. Down at the base of the banister, a heavy hex nut on the anchor flange had backed off by a quarter turn, allowing the whole steel post to rattle slightly against the concrete floor. That kind of play ruins a solid pivot point. I knelt on the cold slab, retrieved a flat metal bottle cap dropped behind the fire door, and slipped its crimped rim directly into the gap beneath the loose bolt head. Throwing my weight down with both palms, I jammed the metal shim tight. The wobble vanished completely. Now the turn onto the floor is rock solid.