The Key itself moves in a "seesaw" type of motion as the player presses the front end. The key coverings of modern pianos are no longer made of Ivory due to legal restrictions on its use. Most manufacturers now offer some variety of a man-made or synthetic ivory to provide a touch sensation that some players feel is conducive to smoother piano technique.
Key Leads are used to balance the key's "seesaw" motion so that just the right amount of force is required to press the key down. Since the keys of the piano become longer as you approach the lower notes, lower notes require more key leads than higher notes so as to make all keys feel the same to the player. The key leads must also be positioned very accurately since the closer they are to the front of the key, the easier the key will depress and vice-versa.
The Key Button is made of very sturdy wood in order to resist wear from the constant movement of the key on the Balance Rail Pin. The Balance Rail is part of the key frame (not shown) and supports the Balance Rail Bearing which serves as the pivot point for the "seesaw" movement of the key. The vertically adjustable Capstan Screw does the actual pushing up of the other components of the action.
The Action Hanger is mounted to the key frame (not shown) and supports three separate rails that each have certain action parts attached to them as you will see below.