This sale is for a Mamiya RB67 / RZ67 Eye Correction Lens -1.5 Dioptre for the standard RB ProS and RZ type waist level finders, complete with original box. This is the standard dioptre supplied with all WLF; use it to replace a non-standard dioptre or buy it if your dioptre is missing.
This dioptre simply clips into the waist level finder. This dioptre is in mint condition but the wrong box (the box says 0D). It was no doubt removed from a new camera at the time of purchase and has never actually been used.