The spacer pins in the cylinder are a master key setup. If there were more than one in each cylinder that means that there was probably more than two keys that went to that lock. As far as the 6th hole not having any pins that could be for a few reasons, one it could be because they are only using 5 pin keys so the 6th pins is not necessary or it could be that they are using 5 pin keys and 6 pin keys and that lock was on a say front door or a storage room where everyone has a key to it. So the people that have low keys( keys that open there office and that door etc.) only use 5 pins keys but higher people ( janitors, owners, etc) have 6 pin keys that open more doors than just those 2.
I have seen cylinders where the 3 or 4th pin stack is missing because there are so many keys that have to open that lock you have to leave a pin stack not used to get so many keys to work on it.
There are many different size wafer pins ( or spacer pins as you called them) that they can use, so many different keys can work on the same lock but not on others in the building.
My question is why the little disks? And why so many spacers. wouldn't you really only need one for a different key
It all depends on how many keys had to goto that lock. Maybe he had a key the janitor the owner, manager who knows.
Here is a quote from somewhere else that i think might help you understand a little bit:
Some locks are designed to work with two different keys. The change key will open only that specific lock, while the master key will open that lock and several others in a group. In these locks, a few of the pin pairs are separated by a third pin called a master wafer or spacer.
When three pins are combined in a shaft, there are two ways to position the pins so they open the lock. The change key might raise the pins so that the shear line is just above the top of the master wafer, while the master key would raise the pins so the shear line is at the bottom of the master wafer. In both cases, there is a gap at the shear line and the key is able to turn.
In this lock design, the lowest pin would be the same length in each lock in the group, but the master wafer would vary in length. This lets one person, say a building manager, access many different locks, while each individual key-holder can open only his or her own lock.
If you want to lean more just search the forums and there should be enough info on here or the net to explain it.
Here is a little pic.
And take a look at this it might also help you understand the master key system a little more too.
http://mia.ece.uic.edu/~papers/etc/pdf00003.pdf
-James
