As it says in the title. Yours for the cost of postage.
I have no idea what it is for but the instruction sheet with it says it is for Konica Auto-Reflex for mounting Exakta bayonet mount lenses of 38mm mount diameter and 44.7mm flange back.
It is odd though as what is probably the lens mount is a thread rather than a bayonet. The fitting into the camera is bayonet though.
Anyway, it's one of these: http://www.nanites.co.uk/ebayphotos/...dapterII03.jpg
So if you want it, send me a PM and I will only charge for postage.
Due to being annoyed at some other classifieds and free offers limited to the US only, I'm tempted to say anywhere in the world except the US.... but that would be mean and pointless so I will even post it to our English language mangling friends across the water!
EDIT: Looking for information on this, it turns out that it is for fitting M42 lenses to Konica cameras. I have tried an M42 lens and it does indeed fit. So the instructions were wrong!
EDIT AGAIN: The instructions are for three different adaptors. I only read the first one. If I had carried on reading I would have discovered earlier that this is indeed for M42 lenses!
(on the subject of English language mangling, that should be adaptor).