kwikset deadbolt design

[lplink]

I bought a kwikset deadbolt, pulled all the pins out through the top, inserted the key, and looked down through the hull pinholes. As expected, I could see through the row of hull pinholes, through the row of plug pinholes, down to the key. Also as expected, when I began to turn the key, the row of pinholes in the plug disappeared, and I could see just the surface of the plug. But then unexpectedly, with the key turned about 45 degrees counterclockwise, another row of holes appeared in the plug! What are those holes for, and why don't the driver pins fall down into them when the lock is assembled (with pins) and the plug is turned (either with the key or via picking)?

[MrB]

I am told the second set of holes is for contractor keying. They are slightly narrower than the pins, so the pins can't fall into them.

When the lock is first installed, a set of balls can be inserted in the middle of the pin stacks, which stay in the plug when the contractor's key is used. Later, when the homeowner first uses their key, the balls get pushed up into the shell and then fall into the extra set of holes, where they stay forever more. After this, the contractor's key won't work any longer.

If offers a safeguard against unauthorized duplication of the keys while the contractor has them, while avoiding the need for the homeowner to have the locks rekeyed after moving in.

[vector40]

And if there are no balls in the holes, as there probably won't be in any lock you just bought, it's because... well, nobody ever built a house with it and needed a master. It's an optional thing.