by MacGyver101 » 27 Mar 2012 8:35
I'm not sure if you're familiar with Schlage Everest locks, but this is pretty much the same thing (with just a slightly more complicated mechanism).
The extra pin is an additional blocking pin: it prevents the cylinder from turning, unless the "slider" is moved into the correct position. The "blocking pin" moves in the opposite direction to the other tumblers: it's sprung upwards, and normally sticks up through the top of the plug, into the core.
With the Everest cylinder, the side-milling on the key directly lifts the blocking pin. In contrast, this new KeyMark system uses a slightly more complicated arrangement, where the up/down movement of the blocking pin is controlled back the front/back movement of a slider. When a key is inserted, the key's side-milling will push against the slider. The side-milling on the key, if it's cut to the correct depth, will push the slider the proper distance to let the blocking pin fall down (so that it's no longer blocking the plug), and the plug is then free to rotate (if the rest of the key is cut correctly).
It's sort of a hybrid "Schlage Everest built with a Medeco M3 slider" arrangement. The purpose of the mechanism is partly pick-protection, and partly expanded master-keying options -- but mostly patent protection on the keys: it gives Medeco a new key system that nobody else can produce blanks for until the patent expires.
Hope that helps (or at least gives you some more locks to Google for pictures). Looking at an Everest break-down will give you a good idea. (Not to be confused with an Everest Primus: that's different.)
