Having aday.
I need an adaptor ring for my Nikon 105mm...to fit my Lee Filer foundation holder on.
Is this the one I need...linky
Thanks.
If by 'Nikon 105mm' you mean a 105mm focal length nikon lens (like, say, the Micro Nikon 105mm f2.8' then no, the lee quoted number is the diameter of the filter thread, which is probably 62mm.

Nicola is right ,you need this one.
http://www.robertwhite.co.uk/lee-62mm-standard-adaptor-ring.html