If you are trying to save money on a microscope, this is not the piece to downgrade. This component, also known as a bonder arm or focus block, is what secures your microscope to a stand. More importantly, it also focuses the microscope.
Inferior focusing blocks tend to drift - gravity pulls the microscope down and gradually the microscope loses its focus. They can degrade over time and become difficult to adjust.
This genuine Leica component smoothly glides up and down to bring you into a crisp focus, and then it holds its place until you decide to move it again.
This component is especially important with S9 series microscopes. Unlike the A60 series microscopes, the focusing mechanism is not built into the S9. The S9, especially with a camera (the S9D or S9i), is taller and heavier than typical microscopes that jewelers and engravers use. With their 55x zoom magnification in native configuration, any drift will threaten the sharp focus this microscope would normally deliver. Also, stands designed for Meiji microscopes (like the EMZ-5 or EMZ-8) have wider cradles that are too big for S9 microscopes.
Arm weight: 2.1 lbs