This robotic claw arm is great for all your gripping needs. It is small, compact and easy to put together. They are made from metal and are pretty heavy-duty. The claw opens to about 5cm and depending on the servo motor used, it can pick up some relatively heavy objects. Because the arms move parallel to each other, you get a better grip.
These also have a mounting plate on the bottom which accepts standard spacing found on servo mounts (the extra bits that come with our servo motors). The MG995 Servo is the recommended servo for this robotic arm