Every rail run has to end somewhere, and an open tube looks unfinished. The Ball Single Outlet slips onto one 1.5" OD tube end and closes it with a decorative cast ball — the traditional way to finish the end of a stair rail, a bar rail, or a post top with a rounded detail instead of a raw cut. It's an end fitting: one outlet, one clean finish. Choose polished brass for a warm traditional look, polished 304 stainless for a bright modern one, or satin 304 stainless for a softer finish, and match it to the elbows, tees, and other ball fittings in the same 1.5" line so the run ends in the same family of parts.