You may choose to enhance the look of your double open staircase by adding a double volute stair tread to your stairway. If this is the case you will need to know how the fitting sizes are sold for a LH / RH Starting Tread:
Understanding The Sizing Of Double Volute Stair Treads:
The true overall size of a 48 inch ( in. ) double volute tread is: the 48 in. back inside square edge, plus the left side 10-3/8 in. overhang, plus the right side 10-3/8 in. overhang. So, a 48 in. double volute tread ( if the inside fitting size is equal to 48 in., has a total length of 68-3/4 in. ). Note a 45 in. inside fitting size would simply yield a total double volute tread size of 65-3/4 in. ( 68-3/4 in. - 3 in. )
When talking fitting size it is very important to understand that the inside back square edge is all the that matters. So, with a double volute tread this size would be would be the 'out side left side skirt -to- out side right side skirt measurement' or the 'out side left side drywall -to- out side right side drywall measurement' ( if you have no skirts in place ).