The spiky balls, also made of a hard rubber, are amazing! They are
about 9.5cm in diameter. These things can be used anywhere on the body from the neck to the feet (see the free video that you get with every purchase). I have a yellow one and its called Lisa, as I feel everything in life is better with a Simpson’s reference. You can use these standing, by placing it between you and a wall or by putting it on the floor and laying on it, check out the video but there are no limits to the use of this thing. I personally use mine on my back, chest and glutes, and after a hard day, a cheeky roll on the feet will stop you from completely loosing your mind!