Flex rivets are used to attach the TPU gaiter to the boot at the back. Sometimes, if the horse overreaches and steps on the boot, these rivets may break or get damaged. It’s easy to remove and replace the rivets though. You can use a drill or nippers to remove a damaged rivet and then replace it with a hammer, below is a link to a video to show you how to do this.
Flex Rivet for attaching to TPU gaiter to Flex Boot