Medeco pins.
The false sidebar gates are not as deep as the real sidebar gates and they can get caught by the sidebar as you try to rotate the pins with a tool. Since the false gates are not cut deep enough, they won’t allow the sidebar to retract fully and the lock won’t open.
Notice that the chisel points can be either direction depending on if it is a Fore or Aft pin.
Here is a picture that shows the tops of two Medeco key pins. The pin on the right has a small insert pressed into it. I find about one third of the pins from my dozen or so locks have this feature. It’s a couple of extra steps during manufacture. The reason I heard for this was that each hole is drilled to a different depth and the inserts are a different weight than the surrounding metal. The inserts are also different lengths. This supposedly was done in response to a decoding method that attempted to weigh each pin while they were inside the lock and determine their length based on weight. I would like to hear from anyone that can confirm or deny this. I would also like to see a picture of the tool if anyone has one kicking around.
Now back to the serrations. You might think they are there to make picking the lock harder like the serrated pins found in other locks. Look at the picture below and it shows a plain pin along with two different serrated pins. Obviously the pin on the far right would have to be lifted very high before the serrations came close to the shearline.
The serrations are there to prevent the use of the cute little tool shown below. The tool uses a thin wire and slides it up inside the groove along the side of the pin. If tension is held on the lock to prevent the pins from moving, you can feel when the wire reaches the end of the groove on a plain pin and determine the length of the pin. However the large serrations interfere with the operation of the tool and prevent you from decoding the length of the pins.
The Medeco guys certainly do try hard. I wish I had some of the new ARX pins to show…
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