This is the Harken carbo auto-ratchet block mounted on the jib car/slide with the long shackle.  This is useful if you prefer to keep the side deck or seat clear of any hardware.  The auto-ratchet can be substituted by the Harken 009 with a manual ratchet switch (linked below).  If you prefer to keep the jib rigging similar to the standard racing or daysailing Flying Scots you will want to use the block on the slide simply as a fairlead block (linked below) and mount the ratchet on the side deck or seat (linked below).