On the tops and bottoms of iron balusters you can sometimes find what we call shoes. These shoes are decorative pieces that are used to hide the gaps and imperfections left over after drilling holes for your install. They are purely decorative and do not support the baluster structurally in any way.
You install them by sliding them on your baluster, use glue to secure your baluster, then slide the shoe down to hide any leftover gaps.
Here is the tricky part. Do you want to use the set screw or do you just want to epoxy the shoe down?
If you choose to use the set screw, you may have a larger gap on one side of the baluster shoe because the screw does push the shoe to one side. The screw could also come lose over time if your baluster shoes are knocked around. You can choose to ignore the screw and simply use epoxy to hold it into place. This allows you to evenly space the shoe around the baluster to avoid any gap issues, but its much harder to use this method if you are using shoes under the top of the handrail.
When looking at shoes, purchase the shoe that is made for your baluster. 1/2″ Shoes are for 1/2 Balusters. 9/16″ shoes for 9/16″ Balusters. 9/16″ Tuscan shoes are for the tuscan hand hammered balusters. 5/8″ shoes are for 5/8″ balusters.
Keep in mind that just because the shoe says 1/2″ that doesn’t mean the opening is exactly 1/2″. The opening will be larger than 1/2″ because the baluster has to fit inside the hole. A 1/2″ shoe might have a 9/16″ opening. This is to account for any variance in the baluster size and powder coating thickness. Also you can’t squeeze a 1/2″ baluster into an exact 1/2″ hole or you would scrape up the baluster.
Another thing to look out for are using shoes for the hammered balusters. Hammered balusters have some spots that may be 1/2″ and some spots that may be 9/16″ or even larger. They are hand hammered and there could be some variance. For this reason the opening on the shoes for Tuscan balusters is slightly larger and depending on where your baluster is cut and where the shoe ends up sitting the amount of gap left over could be less or more. This will not be an issue and in fact because the hand hammered look is desired for more rustic and Italian style homes it will even give off a more hand crafted look that is preferred by most designers.