Solid Treads Versus Retrofit Caps
Solid treads, usually 1 inch or 1-1/16 inch oak, replace the old treads entirely. They are the strongest and most traditional choice.
Retrofit caps are thinner hardwood treads with an attached nosing, glued and fastened over existing treads. They avoid tearing out the old stairs but add height, which has to be accounted for at the top and bottom step.