2 x 12 Stair Tread Bracket

This is a typical 2 x 12 stair tread attached to a 4 x 12 stringer using a stair bracket installed properly. As you can see the unpainted area around the tread this is due to the lumber shrinking as the wood dries out.

Under Stairs Bracket Supports

Addition Stair Stringer Support

2 x 12 Tread Shrinkage
Weak 2 x 12 Stair Tread