Cold Steel Ultra Lock

As the knife is opened the blade rotates in a around the locking pin via a larger channel cut out into the blade tang. As it approaches the full open position, the spring loaded locking pin moves forward through the straight portion of the tang channel until it "dead ends," locking the blade in place.

To close the blade, the lock the pin is retracted far enough that it reaches the curved portion of the channel, allowing the blade to rotate closed.