The Flex Boot has five ball rivets attached as part of the fastening system; the TPU gaiter that goes around the pastern has one ball rivet at the front for fastening the TPU gaiter strap, and there are two ball rivets on each side of the boot for the back strap to attach to. The ball rivets are secured with screws on the inside of the boot, with washers in between each rivet and screw. We recommend that you check the rivets on your new product, before first use and then at regular intervals to make sure they remain tight. If your horse has a narrow gait and brushes against the ball rivets, we recommend that you swap the inside ball rivets to flat rivets.