I'm trying to strengthen my grip and I was wondering how I would perform this exercise.
Put two plates (start with 10s probably) on their edges on the floor so that the smooth parts are facing outwards. Grab them in a "pinch" between your thumb and fingers. Then pick them up and hold for a certain amount of time.
Another way of strengthinng your grip, is to get a tub full of rice and just stick ur hands in there and squeeze the shit out of it.
Hope this helps,
You're probably best off starting this with two hands. Place the plates so the hubs and the writing are facing each other and the smooth sides are out. Pinch with both hands so your thumbs are next to each other. Squeeze the plates together and lift them. For lighter weights you can stick to one hand, but I doubt you'll pinch two 25s with one hand before you double pinch two 45s.
A similar exercise would be a Hex Head Hold, if you have the right dumbbells.
4 or 5 ten pound Oly plates is good, two 25 pound plates is very good and if you can do two 45 pound plates that is considered a world-class pinch lift!