I had bought a new brake disc a few years ago when the disc seemed to be bent but had managed to straighten it so I had a new disc and felt it was time to press it into service.
The disc is 190mm diameter.

I also replaced the Rear brake brake pads with genuine Magura Pads.

The brake calliper was rubbing on the inboard side so I added an extra spacer washer making 2 washers on with top and bottom brake mounting points.