(Click here to see an animation of the upright action in action.)
The action pictured here is a full upright (any piano 51 inches high or taller). Consoles and studio uprights (direct-blow pianos between 39 and 51 inches tall) do not have parts 41 through 45. The capstan screw (#46) directly contacts the bottom of the wippen (#39)
Pianos smaller than 39 inches high are usually spinets, which are identified by their characteristic indirect-blow, or drop, action.
In a spinet (pronounced "spin it"), the action drops below the level of the keys, whereas in a console or taller piano, the action sits on top of the keys.
The spinet action is referred to as indirect-blow because of the drop wire attached to the back of the key connecting to the elbow attached to the wippen below, whereas on direct-blow actions, the key contacts the action directly.
Some spinets have original plastic elbows, which can eventually become problematic. The original elbows (usually white or off-white) were made of early plastic, called bakelite, which does not stand the test of time and eventually they disintegrate. A broken elbow manifests as a key that stays down and will not play the note if it is lifted. Elbows made of wood or clear plastic (which are new replacement elbows) will not be problematic.