What is the metal piece that moves the stirrups up and down on a western saddle called?

I lost the metal part on the western stirrup that moves them up and down. I was wondering what that piece is called and where I can find one?

Not all western saddles are made exactly the same. Do a google search for "Western Saddle parts" and you will find a number of diagrams with the parts labeled. You can order the parts online.