The problem: Wooden stringers are endgrain and won’t hold a screw and the triangle wants to break off with the grain anyway, this makes the steps warp and rock back and forth.
 
Solution: Stair Saver screws into the continueos part of the stringer and up into the step and riser. eliminating the triangle and locking down the stairs and riser.
These are solid 1/2 inch square steel bars, if you ever want to replace the stairs entirely just re-use them to make new stringers.