Is this railing completer kit for both horizontal and stair railings? In other words, will balusters fit when angled?

Hello, and thank you for your interest in Trex railing. This 91.5" accessory infill kit for square composite balusters in the color Rope Swing is designed for a horizontal application only. The stair infill kits are sold individually as the brackets will differ and the baluster spacer holes will be more elongated in a stair infill kit for a stair slope. The Lowes model # for the stair infill kit with these same features is 870338. I hope this helps! Thanks, Tori - Trex Customer Care Team