Taylor Hobson Cooke 12 1/2" 320mm f5.6 Series VIII Lens [EXC-]

This is a highly desirable Cooke 12.5" Telephoto. It seems like it was meant for a large format camera, there is a lock ring for mounting, but I am not sure what it is meant to cover, possibly 5x7.

There is a small mark on the front element and a big nick on the rear (see photos). The aperture works well and turns smoothly.

The lock ring is included.