This is a pair of New Satin Brass desk knobs which include the screws to attach them to the keyboard cover of your piano. These are designed specifically for a piano. The dimensions of each knob is 5/8" in height with 5/8" in diameter.
Please choose the type of screw needed. Either machine screws or wood screws are available. If the screw comes in from behind the fallboard, then the machine screw is what you need.