Deep Tissue High Desity Spiky Massage Balls (Muscle Relief and foot / back massaging) By Pro-fitness Source Pro-fitness Source High-density massage balls: This grey one is firm and high-density, which is mainly used for massaging and tissue relief. Diameter of Grey massage ball: 9.5cm (3.7"), Spiky outer layer offers stimulating effect, increasing circulation Packed with firm white box. A black sports bag is enclosed. The Stronger Spiky Massage Ball is perfect for plantar fasciitis, muscle soreness and pre and post exercise trigger pointing. We are sure you will take this massage ball with you wherever you go.