In the construction industry, there are many standard codes and regulations for installing railing or balustrade. One of the most well-known codes is the 4" Sphere Code, also known as the 4" ball rule. This Code states that spindles or balusters must be spaced close enough together so that a 4" ball cannot pass through any given space in between each spindle. Each of our spindles and balusters come with a recommended On Center Spacing. This measurement is designed to space the spindles as far apart as possible, while still passing the 4" ball code.