Stress Ball - Available in 4 Strengths, Injury Rehab & Stress Relief - Grip Strengthy Squeeze Training for adults and Children/kids-Set of 4 Resistance. MAKE EXERCISE SIMPLE – These colorful stress relief balls in three levels of progression (15kg-20kg - 25kg- 30 kg resistance) can improve finger and grip strength for athletes (rock climbing enthusiasts, fitness, tennis, baseball, boxing, tennis, golf and shooting) and musicians (guitar players, bass players, pianists and violinists).
eBay