Steel Box StructureRound Staircase SIZE dia.:≥Φ2000mm (designed according to stair opening dimensions) steps:customized by floor-to-floor height (finished floor) SPEC. Stringer:steel box structure Q235, 4mm thk Treads: /American red oak, 20mm thick /European beech, 20mm thick Risers: /American red oak, 20mm thick /European beech, 20mm thick Handrail: stainlesssteel304#, Φ38mm/Φ50mm Rails: stainlesssteelsolid bars, Φ8mm, 5 lines Balusters: stainless steel 304#, New Style "Steel Color:" /shiny silver /black silver/titane cuir / Red/ White/ Black Stainless Steel Finishing: /Polished ( mirror ) /satin ( brushed ) "* GB Q235 is conventional steel, equal to DIN S235, ASTM A570. * stainless steel we used is AISI 304." Send us your house floor plan or photo for a free drawing to see how this staircase will fit and look in your home or shop. Xinding specialized 7 years in design & making steel staircase. To help you upstairs step by step on staircase we make is what we untiringly aspire after.