I found it at a yard sale. It's cheap. Does it look worth purchasing? I usually brew my coffee in a percolator (or is it called a mocha brewer?), so I'd like to use it for that.
It looks like a burr grinder, as opposed to a blade grinder. Burr grinders give a more consistent grind size, which is why they're preferred over blade grinders.
My guess is it's made of steel, but it does look tarnished. You might take it apart and polish it to create a smoother grinding surface.
The wood on the inside might be difficult to clean of coffee oils and impart an odor to your freshly ground coffee.
I can't tell if the mechanism has a means of changing the grind size. If not, it may in fact be an old spice mill. Otherwise, it won't allow you much variety when grinding your coffee.
If it's given a little TLC I think it would make a nice vintage manual grinder. Compared to blade grinders, even this older grinder ought to do a better job than they ever could. However, if you can't change the grind size than you'll be limited in the type and quality of the coffee you can brew using it.