All elastics are made with the same high quality latex and are available in four different sizes.The outer diameter and the diameter of the inner hole have been designed to optimize the kinetic energy and loading effort. The result is a wide range of elastics that cover every need. EXTERNAL DIAMETER: 20 mm EXTERNAL DIAMETER: 18 mm INTERNAL DIAMETER: 4 mm RING NUT: M14X1 (standard for 16 mm tires) RING NUT MATERIAL: Grivory Plastic GV5H