When attempting to mount my Garmin Nuvi 650 GPS unit in my car - I found it was hard to find different mount options to permanently mount the unit because the Garmin Nuvi uses a craddle to mount which you must use to feed it power. The craddle uses a ball socket design - so the trick is simply to find a compatible ball joint with the characteristics you want. The ball socket is compatible with 5/16 inch ball joints. The unit comes with a suction cup mount and adhesive discs which can be used to mount it to non-smooth surfaces. In my case, the standard mount was too big and pushed the unit out too far. If you want to know about compatible, alternative mounts - read on!
This mount is shorter then the included one and is non-adjustable. However, in my installation, it still proved too tall. Below is a comparison photo between the included adjuatable mount, and this part. Note if you search for Nuvi compatible parts, this is often the only other that comes up. This is listed as a 'fixed dash' mount.
This mount is even shorter then the other mount and is IDEAL for the minimum depth install for the Nuvi if the mounting point is to be behind the unit and you still wish to use a suction mount. When connected, it leaves about 1/4" of depth behind the antenna. This is NOT listed as a Nuvi part, but works perfectly. Below are some photos to show the size and comparisons.
A Sample install, including comparison photos and installed photos
using the -10 part can be viewed Here
This Garmin uses a screw-on mount with a universal AMP mounting pattern for its screws. This mount seems PERFECT if you are screw mounting it to a surface behind the unit. The problem is you can never find dimensions on it! But now some owners have posted photos of their install, and I've mirrored them here for your comparison. Check Here for the full set of photos, including component and installed photos.
A sample install using this part can be viewed Here
The RAM mount is your option if you are looking to physically mount the unit with no arm or block at all. I used this mount with a fab'd block in my car because I did not have the size references for the Garmin mount listed in Option 3. Option 3 would have been an alternative to the install I did in my car using the RAM mount. Photos of my mount using the RAM mount can be found Here
And here is a photo showing Option 2 and 4 vs the included adjustable mount
These parts can all be found online for less then $15. I originally got my pieces from MountGuys.com and they treated me well including an exchange when Option #2 didn't work for me.