a constant velocity joint includes a shield to protect a j - boot from damage due to projectiles such as stones and to prevent ballooning . a rigid portion of the shield is fixed to a ring , which is adapted for fixation to a powertrain component such as a transmission . a flexible portion of the shield prevents projectiles from entering through the opening created by non - coincident axes of the shaft and ring . the flexible portion has a number of truncated conical panels with alternating orientation that accommodate the variable size opening by flexing in an accordion - like fashion .