Hello, And thank you for your question !
The building code reuirememnts for ballistars (pickets) on both stairs and deck/balconies is 4 inches in the opening. No object larger than 4 inches in diameter mey be able to pass through the opening of a ballistar. This was instituted because of kids and animals getting stuck between them (their heads)
I hope this answers your question, if so please click the green accept button. If not, Im still here to assist you.
Is this written in the National Building Code and if so where can I find it?