That type of set up is often used with a roller furler.

:: Looks to me like some sort of turning block. If so, then
:: perhaps a previous owner installed it in order to keep
:: the jib halyard in line with its corresponding masthead
:: sheave. Not at all necessary, however.
::
:: :: Hello,
:: ::
:: :: I was looking at my mast the other day and noticed this
:: :: thing near the masthead. It looks to me like the Jib
:: :: Halyard should be routed this way, but maybe it is just
:: :: a fair lead. I haven't dropped the mast as of yet, would
:: :: like to do it in the Fall.
:: ::
:: :: I am contemplating setting my boat up for a spinnaker,
:: :: thus the scrutiny from afar.
:: ::
:: :: Please see link to image:
:: ::
:: :: http://www.keay3.net/masthead.jpg
:: ::
:: :: Thanks,
:: ::
:: :: Keay
::
:: :: S22 "Dayspring"