The dart shaft silicone rubber 'O' rings are used between the dart barrel and the dart shaft. The rubber O rings keep the darts shafts from becoming loose. Suitable for all 2BA steel, alloy and aluminium dart shafts and are made from a high quality silicone rubber compound for maximum performance.Silicone Rubber O ring Specifications:Outside Diameter: 4.5mmInside Diameter: 2.5mmThickness: 1mm.Each pack contains 3 x silicone rubber O rings.