The HD Flex™ Fiber Enclosure is 4 RU and is configured to accept 12-port HD Flex™ cassettes. The modular design accepts up to 24 HD Flex Fiber Cassettes or Fiber Adapter Panels for a maximum density of 576 fibers. The HD Flex™ Fiber Enclosure is 4 RU and is configured to accept 12-port HD Flex™ cassettes. The modular design accepts up to 24 HD Flex Fiber Cassettes or Fiber Adapter Panels for a maximum density of 576 fibers.