The code required that a four-inch round sphere should not be able to pass through any part of the spindle system, so I cut two spacers at 3¾”. The spindles were used with the horizontal spacing at the top and the bottom and one can start at any one of the 2x4 spindles and work toward any direction. The vertical elevation was dictated by the bottom of the outside finger grips for all spindles. To nail these on, I used No. 8 penny or 2½-inch, exterior-grade nail. I personally like to use two three-inch, ring-shank, exterior-grade nails at the bottom of the spindle and I like to use two ring-shank, 2½-inch, exterior-grade nails at the top.