What is the name of the piece that is often used to switch gears? I have been trying to find this part on BrickLink and have searched every Technic category.  I have come up empty.  

Could someone provide the name of this part so that I can find it on BrickLink?
That is Part 6641 - Technic Changeover Catch.

Also known as "Technic Transmission Changeover Catch".