A stair stringer (also known as ‘string’ or ‘stringer board’) would be the housing on both aspect of the flight of stairs, into which the treads and risers are mounted. Staircase stringers may be created to ‘home in’ or cover the sting with the stairs from see, or cut and https://stairfactory.co.uk/Products/staircase-with-a-metal-stringer/