about the link in the red at the top center (in the photo below)?

If so, there is one on each side. I connect a bridle to it with 2 lines aft on each side. One line goes to the boom and one to the base of our boom gallows. It keeps everything in alignment as I use the boom and mainsheet to lower the mast for trailering. You can see it in action in one of our Youtube videos at;
http://www.youtube.com/watch?v=9FcG4H_dQyQ&feature=share&list=UUyGH1-xOhCotpV_zhSzQq7g

NOTE; is you don't have a set of red/cyan glasses handy, click on the red "3D" symbol at the bottom of the video window and turn off the 3D option for a standard video. Once you turn this off, it should not come back on.

Also, when we head out it makes a GREAT spot to store our boat hooks. The point goes into the D ring there and I have lashed on a 2 inch SS ring on the stay up a few feet. I slip- the boat hook handle through the ring, then lower the point in. So far, we have not lost one single hook!

Greg