Lsgoodcare Convenient 4 Levels 30, 40,50 & 60 lbs Full Set Silicone Exerciser Gym Hand Finger Forearm Strengtheners Trainer for Men Excellent Use At Home, In The Car Or Where Ever You Are Material: environmental protection silicone with soft, non-cracking , long life, does not irritate the skin and so on Outside Diameter:8.8cm, Inside Diameter: 4.5cm. 3 weights Exerciser Gym: green one: 30LB black one:40LB red one: 50LB You can easily change your grip to bias the resistance to different fingers, and by the time you get to where you can squish the red ones with authority, you'll have quite a grip. They can also be used isometrically to activate the adductors on the back of you hands, by pushing your fingers and thumb into the hole and then opening them against the donut. On the lighter ones, you can also work your thumb independently. Very simple, yet effective hand grip training devices. No springs or anything that can break or scratch. And they are small enough to keep with you in your work bag or on vacation so you can always work on your grip strength