Spindles, also called balusters or pickets, are the smaller vertical members of a railing panel that fill in the open spaces between railing posts. In the context of wood railings, spindles are often used without any posts, since the spindles are secured to the deck framing and are strong enough to support the top rail without posts.
When it comes to aluminum railing panels, spindles are secured to a top and bottom rail, which makes up a "railing panel", which is then secured to posts with hardware on the ends of the top and bottom rails.
When aluminum railing panels are designed for stairs, the spindle's connection point at the top rail and bottom rail are hinged or cut at an angle to allow the panel to be installed to match the angle of the stair, while allowing for the spindles to remain vertical and plumb.
