Check wall and floor brackets, if present. Vertical balcony railings are attached to a horizontal banister; check the ends of each railing to locate brackets that may be loose.
Screw loose brackets back into the wall or floor as needed by applying a screwdriver (Phillips or flat-head, depending on screw type) and twisting it to tighten the screws. Replace any missing screws.
Grip the banister or rails with your hand and apply pressure in an attempt to move the railing. If you notice movement or noise, you'll need to do additional tightening and maintenance.
Measure the thicknesses of all the vertical rails, if they are not uniform in size, and record the measurements.
Add 1 inch to the measurements to find the right length for the 1/2-inch carriage bolts you need to complete the project. You'll need one bolt, one nut and one washer for each rail post.
Predrill 1/2-inch holes into the rail posts with a power drill, near the base of each where it meets the deck or the horizontal foundation bar that supports the rails.
Drill a 1/2-inch carriage bolt into the base of each railing to secure it to its foundation. Angle holes as needed to avoid joists and obstructions.