How does this key work?

[Engineer]

I followed a link from one of the other posts on here and found some very interesting puzzles. Following those puzzles for fun, I found this key:

http://pzphotosan156-9gr.blogspot.com/ (nearly half-way down page)

Sorry to appear dense, but what is the benefit of this key? Apart from anything else, the screwdriver slot in the end would appear to allow anyone outside with a screwdriver to gain access? I know I'm missing the point to this key completely, but for some reason today, I can't seem to think how it would be used?

[Solomon]

I doubt something for blocking the keyway would be cut to actually operate the lock, after all if someone wanted that option they'd just use the key itself. It'd be even easier to open with one of those on the other side since, as you mentioned, there's a nice little slot to accomodate a screwdriver... no fancy key turner or skills required. I don't see any point to those things whatsoever, it'd keep out the drunken ex who sneaked a copy of the key and decided to join you in bed some night but not much else.

[Engineer]

I meant to mention that it looks to be for a warded lock, not a lever lock, so it's quite old.

I suppose it's short with a flat bow, as perhaps a long key can catch and rip your clothes as you brush past a door? All the same, it looks difficult to turn and why would you want a slotted screw in the other end?

I know I'm missing something, but some days, life escapes me...!

Thanks for the help!

[Stonebreaker]

Someone who knows about these doors told me that most pocket door keys had some means of adjustment to allow them to remain in the keyhole and not protrude beyond the cup portion of the escutcheon plate. The one pictured was Corbin’s idea. When you loosen the screw all the way you will see a much finer threaded stem. Turning it in or out would adjust the length. The larger threaded cap was then screwed back in to secure it at that length.

[Raymond]

I have never seen one of these before so I am just guessing.

I think the handle with the square shaft may separate out of the rest of the key which stays in the lock. ???