Standard sized mortise cylinder with a fairly easy to navigate keyway, but as you can see has a few dimples on the keys.
Those dimples control these 3 sleeves on the plug. They are not spring loaded or anything, just held in place by a thick lubricant/grease.
When picking this lock your tools will usually bump the small tips of these sleeves that protrude into the keyway, causing them to press outward. When you do finally get the lock picked, they protrude out and actually wedge themselves into the top pin chambers, effectively locking the cylinder at a 11 or 2 oclock position.
This can usually be remedied by putting pretty heavy tension on the plug and using the back side of a half diamond pick to push the tips of the sleeves back down, letting the cylinder rotate.
All in all, not a bad lock but not nearly as 'high security' as it looks at first glance.
