The manual focus versions of the 105mm Micro Nikkor have maximum magnification 1:2. The newer autofocus versions attain 1:1.
The optical center of a 105mm lens needs to be about 210mm from the subject to attain 1:1 magnification. The extension can be completely provided by the helicoids (if it has that much travel), extension tubes, bellows, or any combination of these.
This assumes that the lens is used facing forward. Reversing a lens often places the optical center at a different position altering the magnification. It can be difficult to predict how reversing a lens affects the magnification, depending upon the position of the optical center of the reversed lens.