This sale is for one really excellent condition Canon +2D dioptre but it fits all M645 prisms perfectly. I have other dioptres available, and if you cannot see what you want just ask.
This dioptre simply slots in to the back of the viewfinder on your M645 prism, PD prism or AE prism. Please note that it will NOT fit the later Mamiya 645 prisms. It has only very minor signs of use
Note that this dioptre is not suitable for the later Mamiya 645 prisms for the Super, Pro and ProTL. Waist level finders and other prisms need different dioptres.