This sale is for a Mamiya RB67 / RZ67 Eye Correction Lens -1.0 Dioptre for the standard RB and RZ type L2 and PD prisms, and the RZ67 Pro and Pro II AE prisms.
This dioptre simply clips into the prism viewfinder. This dioptre is very clean with minimal signs of use, just faint cleaning marks around the edges, which have no effect at all on use.