Slide the Achieve XP Recurve Sleeve-Lock Block into the windage block on the sight and lock it into the same position using the machined detente.  Add your preferred aperture to the Achieve XP Recurve Sleeve-Lock Block and tighten it with the screw located on the front of the block. 

This can be easily interchanged if you want to have different aperture choices set up and ready to go at a moment's notice.  This is standard on the Achieve XP Recurve sight, but can also be used on the AX Series sights and the Achieve Series tournament sights.