What are those grippers you are talking about ?

The captains of crush grippers (CoC) look like this :

Those are the ones I have

Notice that each gripper has a number in the ends of each handle

The numbers tells you how much resistance the gripper has. The levels that exists are :

G (60lbs), S (80lbs), T (100lbs), 1 (140lbs), 2 (195lbs), 3 (280lbs), and 4 (365lbs).

G = guide, S = sport, T = trainer

This is an example of how to close a gripper , the example here is a CoC #2 being closed :




A tip to get a more consistent exercise : Use the gripper with same orientation all the time. When you look at the spring, you will notice that one of the "legs" from the spring is straighter than the other. The handle with the straighter leg ( dogleg if I recall right ) is the one you place closest to the thumb.

There exists other brands of grippers, but the CoC are the ones I have and am familiar with.