Double return stair treads are always measured by the throat dimension the length between the two mitered returns.
Stair tread return length.
A 42 left return tread is 42 long overall and has a 40 3 4 throat 42 tread 1 1 4 return return this is a 1 1 4 solid stave that is bullnosed on one side and glued to fit along the open end of the stair tread.
Single return treads are measured by the overall length.
Returns can also be added to existing treads as molding.
The stringer is the backbone of the structure.
There are three main components in a standard staircase.
Because the mitered returns are both 1 wide the overall width of a double return stair tread will always be 2.
Stringers risers and treads.
Simply choose a length of return that matches the thickness and type of wood as the tread rout shape as desired cut to length and attach to the tread using a biscuit and glue join or a finish nailer.