A balance rail pin is a metal pin that is inserted into the balance rail. Its purpose is to house the key and act as a pivot for when the key is pressed. They are usually made of nickel plated steel, and are circular in shape. The key is inserted into the balance rail via the mortise at the centre of the key. The pin then keeps the key in place, and kept secure via the key bushings. When the key is pressed the balance rail pin acts as the fulcrum point for the levering of the key.
Balance rails are drilled with pilot holes, then the pins are tapped into the wood. The pins are all equal size, mass, and are inserted at the same place relative to the key. The sharps or black keys, have their pins offset as the length of the key is shorter and therefore the fulcrum point is closer to the action.
Balance rail felt punchings with a hole in the centre are added onto the balance rail pin. This prevents knocking and clicking of the two wooden surfaces of the balance rail and the key. Often, paper shims are added to even out the key height of the keyboard.
Balance rail pins can be polished, and lubricant such as Protek can be applied to help reduce friction between the pin and the key bushing. If the friction is so high that the key is heavy or slow, then easing the balance rail mortise can improve this.
A similar, but larger pin is found on the front rail of the piano. This is called the front rail pin.
