Which version of the lens did you get? The Leica Thread Mount version uses the simple Thread Mount to M Mount adapter, I use a Voigtlander adapter- sold by cameraquest.com.
There are also versions for Nikon S-Mount, Contax Mount, and F-Mount. The adapters for these are expensive- ~$300.
The RF versions of the lens - front row. You want the Leica Thread Mount version on the Left.
I did not photograph all of my 105's...