This is the Stability-Enhancing Alpine Link for the Marin Rock Springs and Tara Quads. I bought it for my 2004 RS, but I believe it fits the Rock Springs model year 2004 thru 2006.

When you could find these they sold for $80. Selling for $50 + $5 shipping or OBO.

http://classifieds.mtbr.com/showprod...?product=46228