The O-rings were two rubber rings that formed a seal between two sections of the SRBs. The sections of the boosters were joined using tang and clevis joints and the rings were intended to seal the joint while allowing for the inevitable movement between the sections under flight conditions. By design, pressure from within the booster was to push a fillet of putty into the joint, forcing the O-ring into its seat. The system never functioned as designed. The rings were supposed to sit in a groove and seal the joint between the sections of the booster. It was found, however, that flight dynamics caused the joints in the SRBs to flex during launch, opening a gap through which rocket exhaust could escape. As the joints flexed, the rings would come out of their grooves and move to a new position in the joint, a process called extrusion. The extruded ring would form a seal in this new position, but during the time it took for the ring to shift, the joint was unsealed and hot gases could escape, a process called blow-by. These hot gases damaged the rings until the seal was achieved.