Mystery Dioptre Sight

[Troubledshooter]

Whilst sorting through some spares, I found this diopter sight and haven't a clue as to what it fits. It appears to fit an approximate 12.5mm rail.
There are no makers marks on it that I can see, but the large thumbwheel at the front may give a clue to someone.

[I. J.]

Im also interested in the replies as I have a couple of sets which Ive marked 'HW'

[lightning22]

HW is the first name that comes to mind with that one.

[zooma]

That looks just like the diopter's that I have fitted to several of my old HW target rifles and from the measurement you quote it is probably one of the older size to fit the wider 13mm scope grooves .?

The large thumb screw engages into the prominent recess positions on the HW rifles to make a very secure recoil stop.

[Garvin]

Defo a Weihrauch, as said, and for older 13mm rails by the looks of it.

[Troubledshooter]

Thanks for the replies, so Weihrauch it is and definitely to fit the 13mm rails. I thought the front thumbwheel screw might point to it's origin, and would locate into a hole somewhere on the action.
Second question, what's it worth ?

Here's a picture I found of the sight fitted to a HW35, but mine has the rubber eyepiece as well:

[MDriskill]

For what it’s worth, here in the US a good HW diopter is worth around $100.

Whatever the going rate is there, that example is worth a premium due to the excellent condition and rarity. Since the late 1970’s HW’s grooves have been spaced at 11 mm, so the 13 mm ones are sought after by collectors.