The close up lenses are called PROXARs. They come in 3 strengths.. +0.5, +1, and +2. The diameter is set in mm, and generally, if your lens is chrome or uses a Compur shutter ( C lens) , you want a B50, and if the lens is black AND HAS A PRONTOR Shutter ( CF Lens), you would want a B60. If you lens has NO shutter ( F lens), then you want a B70. They were and are made by Zeiss ( for Rollei) or Hasselblad. Either make will fit your lens.
Extension tubes are more money....they come in lengths of 8, 10, 16, 21, 32, and 55mm. At least from memory that is correct. The 10 and 21 and 55 are older and less costly ( no reason, ths is is just the way it is.)
There is a lot of overlap between ranges ( with close up thingie or wothout) using either setup. If you know what distance you wish to shoot, email me and I will look up your combo of lens plus distance and tell you which item specifically to get.