This fits to the windscreen or to any flat smooth surface, and has to be totally flat or will not create a vacuum and stick.
Having said that, once it is stuck it is sturdy and holds any size iPod, PDA, Mobile phone really well.
The sides work on a ratchet system and you press the button on the back to release them to their greatest width. Then you place in your iPod, push one of the sides closed and the other will close at the same time, until they are holding your iPod nice and firm. Solid as a rock, well designed and a must-have!
I bought a cheaper one, was disappointed and then thought "blow it" and forked out for this. I would buy one as a gift and I would definitely recommend it.