I have designed a little different gripper from the ones that are already uploaded.

It works with this servos http://www.miniinthebox.com/mini-9g-servo-with-accessories-translucent-blue_p638990.html

You just need to print it and use a screw that is already shipped with the servo, so you don't need any additional hardware.

Use example: http://dai.ly/x2do50f