This sale is for a good condition Mamiya 645 Super AE Prism Finder N, but with faulty metering so therefore probably only usable as a non-metered prism. It is suitable for use with the newer Mamiya 645 Super, Pro and ProTL cameras and will not fit the earlier M645 models.
This prism is actually a faulty Super AE prism. The metering displays the set shutter speed (so still more useful than a standard non-metered prism) and the meter responds but is many stops out (maybe shows 1/500 instead of 1/2 very approximately). The shutter speed display in the viewfinder works fine so it correctly indicates the set camera speed, and the glass is just about perfect. This would be great as a standard prism.
Instructions for this prism can be downloaded from this website. Note that this prism does not have a working light meter.