Finding the binding order is one of the first steps to picking a pin-tumbler lock.
When applying rotational tension to the plug within the cylinder of the lock, it will force the pins to "bind" making them seem stuck or hard to move.
Manipulating those binding pins first will put you on the path to finding the sheer line of the lock, allowing you to rotate the plug completely, thus opening the lock.
If the order in which the pins are binding have been memorized, then, in theory, you should be able to manipulate the lock a second time, in the exact same order. This is the binding order. It is also believed that you cannot open the lock until the proper binding order had been achieved.
Below are my concepts and theories on finding a binding order for any given pin-tumbler lock:
Use this tutorial with North American Pin-Tumbler locks in mind. In North America, our pins are stacked at the top of the plug, with the key pins are below the driver pins, and the driver pins are below the cylinder springs. This is the opposite in most European locks, but it is really only relative to how the lock is installed into the door itself. But this tutorial is primarily discussing locks as they are applied in North America.
In lock picking, there are two natural occurrences that produce a binding order of a lock. The first is the placement of the holes drilled into the top of the plug.
Depending upon the quality of manufacturing, these holes can be minutely staggered, hardly noticeable to the human eye. However, that discrepancy is there, which means not all the holes are aligned perfectly. The one pinhole that protrudes the furthest from its intended centerline, will be the hole that contains the pin that will bind first. This is all depending on two smaller details. One factor being the rotational direction of the plug (clockwise or counterclockwise). The other factor is the placement of the holes in the cylinder itself, and how they align with the holes in the plug, as there are two different parts to every lock… the plug, and the cylinder.
The second natural occurrence of binding order in a lock is produced from the type of tension applied to the plug itself. If applying bottom of the keyway tension in a clockwise fashion as the lock faces you, then the lock will find a natural binding order that is relative to that type of tension applied (being bottom of the keyway). But if we apply counterclockwise rotation, while using bottom of the keyway tension, then you should get a completely different binding order of the pins in the lock.
The same goes for adding Top of the Keyway tension (TOK), for both clockwise and counterclockwise tension. So we have come to find that a lock can have up to 4 different binding orders just from the different types of tension we apply to it.
That is why I have stated that there is no such thing as a 'natural binding order' because we are manipulating a specific binding order that is only relative to the type of tension applied to the plug itself.
I also don't agree with the statement, "the binding order of this lock is..." because there is no singular binding order to be found at all.
Further details of manipulating the binding order are discussed below.
The Lever Effect
If using Bottom of Keyway tension (BOK), it will cause a pivot point in the middle of the plug, almost like a fulcrum, thus making a seesaw or teeter-totter out of the plug itself, as it sits inside the cylinder.
The tension wrench becomes the "load," the back of the plug becomes the "force," the middle is the fulcrum. Thus, if we apply downward pressure at the front of the plug, the first binding pin will naturally be the back pin since it is located at the top of the plug.
This is not absolute, and will not happen every time as it will depend upon tolerances of every given lock. But you are indeed increasing the likely hood of forcing the back pin to bind first by using Bottom of Keyway tension in the front of the lock. The front pin doesn't want to bind first because you are pulling the plug down while applying rotational tension. It's very small in movement, but it's there.
What is Torsion Tensor?
To say that torsion alone is being applied to a plug is incorrect. A brief definition of torsion is: "In the field of solid mechanics, torsion is the twisting of an object due to an applied torque."
You will notice, we are not twisting the plug, we are merely rotating it. Therefore the correct terminology is Torsion Tensor. The brief definition of torsion tensor is: "The companion notion of curvature measures how moving frames roll along a curve without twisting."
So since the plug is merely rolling along the curve of the cylinder that holds it, and the plug itself is not twisting or changing its physical form, Torsion Tensor is the correct terminology to use when describing the action of applying tension to a plug, in a rotational manner. This could be sufficient to say why the British in the UK call a tension wrench a "Tensor" and not a torsion wrench or a tension wrench. They clearly have a better grasp of the physics involved with turning the plug of the cylinder.
The British are known for being extremely accurate in their measurement, so it's always safe to fall upon their descriptions instead of North American terminology as it pertains to locks.
The Lever Effect Continued
Not only is the tension wrench turning the plug, but you are literally pulling down on the plug as well, causing the back end to pop up (very minutely) thus causing the last pin to bind first (typically). If you use Top of Keyway torsion, it's the opposite, and the front pin will usually bind first (because you are forcing the front of the plug up).
The middle pin should be the least affected by this as it is the 'pivot pin' in this lever effect. But it can still be the first binding pin if the first natural occurrence is present, which is the misalignment of the pin holes themselves.
That is what was taught to me when I was an Apprentice Locksmith. All the locksmiths at my shop picked from back to front, then front to back, then randomly, while applying Bottom of Keyway tension. This is because it was perceived that the last pin would bind first due to this lever principle. I have never known or worked with a locksmith that understood or practiced finding natural binding order. They always just used physics to create a binding order from the back to the front or find an order that is dependent upon the tension being applied.
This technique doesn't always work, as all locks and manufacturing processes differ, but it’s a safe place to start when picking an unknown lock.
The Myth of the Natural Binding Order
I was told once, that the only way to find a natural binding order of a lock, the kind most people claim to have found while using Bottom of Keyway tension, could only be done by using a tension wrench so long (on the working end that is inserted into the plug) that it would have to go all the way through the lock and stick out the back. This would allow you to apply completely even rotational tension and pressure on the plug within the cylinder.
That is the only way to find the “natural” binding order in a lock. That’s the actual binding order which was created by inaccurate machining and milling processes.
Pickers think they have the natural binding order, but really it's just the binding order that is relative to the type of tension you are applying to the plug within the cylinder.
In addition, if there was such a thing as finding the “natural binding order” of a lock, and the physics of applying downward pressure as well as torsion tensor (rotational tension) to the front of the lock didn't exist, then picking a lock would be as easy as reading a list of numbers, 1-2-3-4-5, then picking that order, while going down the list... 1-3-4-5-2, 1-4-5-2-3.
This sequence of numbers is called a permutation. There are only 120 possible combinations with 5 digits if none of these numbers repeat.
If the physics above did not apply, and you went through all the possible combinations out of 5 numbers, for a total of 120 combinations in total, you would eventually open the lock without any skill involved whatsoever! But that's not going to happen because on earth we are governed by physics, and you are indeed changing the “natural binding order” and creating a completely different binding order that is relative to these 3 things...
1. Pulling force on the plug itself (down/up, fore/aft, pitch/yaw)
2. Torsion Tensor (rotational tension)
3. And the consistency of both factors listed above
So don’t give up, and create your very own binding order that is unique to the type of tension you apply to your lock.