AXIS TS3901 Rail Extensions allow AXIS S3016 Recorder to be mounted in deep server racks with a post-to-post distance between 499mm (19.6in) and 689mm (27.1in).The original rails can be used and no extensions are needed for server racks with a post-to-post distance between 376mm (14.8in) and 499mm (19.6in).The post-to-post distance is measured between the outside-facing surface of the front and rear rack posts.