Weights in most aspects of Physical Culture is ideal to developing strength and unbelievable power and physique but it's not always the case. In other words, you don't weights for everything unless you're looking for a particular way to build strength. For grip work there's a lot of ways to develop mighty mitts but i'm here to tell you that weights aren't always needed in this manner. I have build a powerful grip without having to do barbell and dumbbell work, I mainly use only a couple maybe three implements that would be considered "weights" but in truth they're just a measuring stick compared to how I really found my grip power.
To truly understand Grip Strength we need to look back to what makes us very strong or very weak in our hands. It takes a tremendous amount of strength to bend steel, rip a phonebook and/or lever a heavy sledgehammer so to really make that strength possible is to not do something else but get down to the dirty soil and reach down and use those actual tools to build your grip strength. Another way of building great grip power without the iron is doing hangs from a bar or rings; these alone can build an insane grip because in order to even hang you need to have a bit of tightness to grip the handle and just stay there. Some can't hold for more than a couple seconds, some can hold far longer its a matter of practice and focus on the intention.
Finger Tip Push-ups is also a favorite since its very basic and simple exercise yet many can't do it due to issues in the wrists or fingers. The objectivity is to utilize what works best for your goals and achieving progress little by little. I love to move around like an Ape and since my mind is getting more geared towards that Tarzan like state and doing Ape style movements I'm doing exercises like Hanging from the pull-up bar in different grips to hit the tendons and muscles from other angles, walking or jumping like a gorilla by being on my knuckles and putting my weight onto them the majority of the movement and building that pull-up power by isometrically flexing in various stages of the actual pull-up. Training the fingers and hands is essential to building a complete body that is full of strength from a variety of angles.
Training to use as minimal equipment as possible without relying the barbell and dumbbells is very effective and its more natural. The Sandbell is one implement that is great for your grip and no I don't consider it weights, this is more functonal and can be used for practically any movement. I believe without question the best of the best when it comes to pure natural grip strength and powerful tendons are mountain climbers, these guys/girls have pound for pound some of the strongest hands on this planet period. They are the closest to our Ape ancestors by having fingers that could literally tear you apart if you fought them. You don't need to be a mountain climber to build this kind of strength but you will need to find a rock climbing wall or build one around your house or for the cheap route get eagle claw straps to wrap around your pull-up bar and go from there, I've tried these and they're tough as hell and I only managed maybe a couple reps the last time I tested them.
Don't believe for a second grip strength is purely getting from wrist curls and weird machines, if you truly want a mighty set of hands, you need to get dirty and do exercises that really target the hands and fingers while engaging the entire body, isolation isn't going to cut it. Its not a knock to anyone but from personal experience and seeing some of the strongest men on the planet within mere feet up close I know for a fact real grip work comes from those who target the hands in a specific manner that digs into the tendons and builds insane eagle like claws for fingers. Train your grip with a vengeance and you'll learn how tough you can really be with the power of a gorilla.