Abstract: The lock allows two members in a downhole tool to be temporarily held together. In an application where mandrel movement is dictated by pressure cycling in combination with a J-slot mechanism, such as in a downhole valve, the mandrel is releaseably retained to an adjacent connector against mechanical impacts. The mandrel features an extended collet that moves relatively to a floating sleeve during pressure cycles. At some point the collet heads rise to an elevated groove that causes them to contact a no-go shoulder for locking. The lock is defeated be removing the collet heads from the elevated groove for normal tool operation.