Check local building code.
If allowable gap between spindle is 100mm then following guideline will help you.
for horizontal guard rail spacing of 4.2 inch is appropriate using 1-5/16" spindles.
4.2-1.2 = 3 Inch (75mm) clear space ( 1-5/16" spindles measures 1.2 inches after sanding)
For inclined stair railing spindle spacing of 6 inch (inclined length) is appropriate using 1-5/16" spindles.
6 x 0.7 - 1.2 = 3 inch (75mm) clear space ( 0.7 is for 45 degree stair angle).
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