Spacers (for optical axis alignment) are parts used when the height is insufficient for the set optical axis. Several sets of different thicknesses are provided so that you can make fine adjustments from a size of 1 mm when performing optical experiments such as microscopes, etc. The spacer for adjusting the height of the optical axis is square, and the side length is 40 mm or 60 mm. It can be installed and used on the opt-station holder. Free size spacers have various shapes and outer diameters, and the height can be adjusted freely within the standard dimensions. Care must be taken because the tapped holes for securing differ depending on the height.