Mamiya RB67 Prism Finder Medium Format Camera Lens

I'm selling an item that came out of my family's storage.
This belonged to a family member who enjoyed photography.

Brand: MAMIYA
Product Name: RB67 Prism Finder
Accessories: Cap

Exterior: This appears to be a part for a very old camera.
As you can see in the photos, it shows signs of use.
I don't know how to use it, and I haven't been able to confirm if it works, so please consider it as junk.

Please be aware that I cannot guarantee the quality of the images or how it functions.
I don't have any knowledge about cameras, so I may not be able to answer your questions.
Regarding the product title, I've written it exactly as it appears on the camera.
I apologize if there are any errors, but please refer to the photos for confirmation.

I searched for similar items on a flea market site and set the price based on those listings.

Thank you for your consideration.