Male Sydney funnel-web Spider photographed November 2004 at the Reptile Park at Gosford. Photo by www.takver.com Released under the GNU Free Documentation License ... Found on http://en.wikipedia.org/wiki/Lynchpin
A linchpin (occasionally lynchpin) is a metal part used in mechanical engineering to prevent a wheel or other rotating part from sliding off the axle it is riding on.
Found on http://www.encyclo.co.uk/local/20708