Holmium Oxide Filter is a type of glass filter that has neutral density level. This testing apparatus is used to determine wavelength precision of spectrometer. Made of PP or any standard grade plastics. The filter is mounted on an anodized holder that has standard diameter. The protective plastic holder of this filter comes in handy to avoid all sorts of damages. Standard of this Holmium Oxide Filter has been checked on different quality testing parameters to prove its flawless feature.