Captains of Crush (CoC) grippers are fantastic for increasing your crushing grip strength. They come in all levels of difficulty so anyone can begin. Although the number is constantly growing, only a short list of people have ever closed the #4. Just so you get an idea of how hard these things are to close, a regular grip trainer you can buy at the sporting goods store is about 15-30 lbs. The CoC Guide is 60 lbs, roughly twice as hard. The Trainer is 100 lbs. The #1 is 140 lbs. The #2 is 195 lbs. The #3 is 280, and the #4 is 365 lbs. Having really strong hands is great for injury protection and functional strength in martial arts. I’d look into picking one up! They’re only 20 bucks a pop.