This Mamiya 645 No, 2 Extension Tube tube is in mint condition and complete with its original (not mint!) box. This tube has absolutely minimal signs of use; it has barely been used.
This extension tube will give you 0.29 to 0.45x magnification with a standard 80mm lens; a copy of the Mamiya instruction leaflet can be downloaded from the Downloads section. I tend to use this and the #1 and #3 rings just to get a closer focus with my 150mm and 210mm lenses – it is so small that it is no problem to carry around in case you need it.