This product is adjustable to provide 0-100kg for you,so it can meet any age of people's need.
Old people can use it to keep their muscle strength for a better living quality, young kid can improve their finger strength to aviod injures in outdoor sports.
Even if you are pro in fitness trainning, this product can also fit your need since it can be adjust to 100KG.
The spring on it is made of carbon steel,which is well known as stronger and heavier than stainless steel.