This sale is for a superb mint condition Mamiya RB67 Extension Tube 45mm (No.1), complete with both caps as shown.
There are absolutely minimal signs of use, nothing at all to see without really careful examination; this tube has barely been used. It has been tested and works perfectly. An absolute bargain with both caps included.
This extension tube will give you 0.35 to 0.72x magnification with a standard 127mm lens.
A copy of the instruction leaflet can be downloaded from the Downloads section of this website that gives full details of usage (essential for correct exposure if you do not have a metered finder).