There is sometimes confusion about terms of saxophone key parts, especially from players who try to post technical questions here. Since this is not my first langauge, I especially noticed all English terms trying to find what I thought were the most logical to use. A few people recommended the terms I suggested as clearest so I am posting explanations and definitions. A moderator will make this a sticky thread soon.
Key: This is a part with a pad. In photo 1, A, B and D together make the key. This is the right side C key.
Lever: This is a part without a pad, that is operating a key from a distance. The part that is operating the C key is called the C key lever (not in the photo).
Post or (less common) pillar: The part soldered to the saxophone, marked E in photo 1, on which keys and levers are mounted.
Pad cup or key cup: This is the part marked D in photo 1. The pad is glued to the key cup.
Key arm: This is the part marked A in photo 1. It is the part that the key cup is soldered to.
Linkage: This is a connection, usually between a key and a lever. The connection between C and A in photo 1 is a linkage. In this case it is the side C lever to key fork and pin type linkage.
Linkage arm: This is marked C in photo 1. This is similar to a key arm but instead of ending with a key cup it ends with a linkage. In photo 1, C is a linkage arm from the side C lever that is operating the side C key using the linkage. In photo 1 A is both a key arm and a linakge arm. In this case the part is usually referred to just as key arm.
Hinge: This is the part marked B in photo 1. This is the part of the key that is used for mounting it on the instrument.
Hinges and screws: There are two types of hinges and (generally) two types of screws. This is where most of the confusion comes from many different terms. Some people confuse by not keeping a consistent term for the same type of part. For example using a term like pivot rod, which I have seen used, is very unclear since it could mean both a hinge or a screw (I've seen it used to mean both).
The most simple definition is: If a part has outer threads on it and a slot on one end, like a screw, and you screw it to the instrument, using a screwdriver, then it's always called... a screw! If it is the long round part of a key or a lever, same as the part marked B in photo 1, it is called a hinge.
The two types of hinges are hinge rod and hinge tube. Part B in photo 1 is an example of a hinge tube. This is a tube where you can see all the way to the other end, as shown in photo 2. Other examples of hinge tubes are for stack keys, palm keys, etc. They are mounted using rod screws (shown and explained later). A hinge rod generally looks similar from the outside but is not hollow all the way to the end, and is a solid rod. It has two holes, one on each end and is mounted using pivot screws (shown and explained later). An example of one end of a hinge rod is in photo 3.
Left side, photo 2: hinge tube
Right side, photo 3: hinge rod
Screws: There are generally two types of screws. Rod screws and pivot screws. Usually, rod screws are used to mount short keys or levers, or several keys on the same rod screw (like stack keys). Pivot screws are usually used to mount long keys and levers.
Rod screws are used for mounting keys and levers that have hinge tubes. This is a screw by the definition explained above, and is shaped like a rod i.e. a long steel rod with threads on one end and a slot on the other end. It passes through one post, goes through the entire length of the key, sometimes several keys and other posts (e.g. stacks) and threads into a post at the other end. Photos 4, 5 and 6 show rod screws.
Left side, photo 4: a rod screw
Middle, photo 5: slot end of a rod screw inside a post
Right side, photo 6: threaded end of a rod screw inside a post
Pivot screws are used to mount keys which have a hinge rod. The posts on both sides are threaded, each to accept a pivot screw, which enters a hole at each end of the hinge rod. Usually long keys and levers use these screws. For example high E and F# keys. There are several types of pivot screws. Photos 7 and 8 show pivot screws.
Left side, photo 7, three types of pivot screws, from left to right: Headless pivot screw, pilot pivot screw, point pivot screw.
Right side, photo 8: Pivot screw inside a post.
There is another type of pivot screw, the pseudo-point pivot screw. This screw has a pointy end, but remains straight almost to the end, unlike the real point pivot screw. This makes this type work the same as a pilot pivot screw.
You can usually recognize pivot screws by having a slot end on both sides of a key or lever, as opposed to the rod screw. Photo 8 (above, right side) shows a pivot screw inside a post. There is an exception to that, this is when a rod screw has the threaded end shaped like a pivot screw. This happens sometimes for stack keys. All keys are mounted on the rod screw except the last, which is mounted on the pointy end from one side and an actual pivot screw on the other, making it similar to a key mounted on pivot screws. In this case you will see a slot end on both sides eventhough one is a rod screw.
Touch-piece: This is the part you actually press with your finger when you play, regardless of whether it is a key or a lever. In photo 9 you can see the low C touch-piece marked with X. Next to it is the low Eb touch-piece. You can see both are connected to their hinges with arms. These would be called touch-piece arms. The name of an arm is decided by the part it connects to the hinge.