See my post below http://cruising.sailboatowners.com/csbb/index.cgi/page/1/md/read/id/166509/sbj/i-replaced-a-clevis-pin-at-the-bob-stay-attachment-with-a-shackle/

As D'Arcy noted, lateral strength is the concern. If used as a backup to the backup, it might just be the thing that saves the boat so long as it doesn't get put under tension until all else has failed.