YYGIFT High-Intensity Wrist Arm Strengthener for Strength Training Bodybuilding Crossfit Material: carbon steel spring+plastic+foam Exercises your forearm,wrist and fingers. Builds the flexor,extensor muscles and improves grip strength. Provides forearm and wrist support for maximum safety and comfort. Please do not overexert when you exercising ,in case of the handle broken and the spring pop up then hurt you or other people .