The NDUV506B is a circular Neutral Density Filter, unmounted, with a diameter of 0.5 inches and a thickness of 1 millimeter. This filter is sourced from Thorlabs, a renowned vendor in the optical industry, and is part of their UVFS series, specifically identified as UVFS Mal-1965.
The NDUV506B is designed with a UVFS coating on both the front and back, specifically the THo NDUV OD06 coating. This coating is responsible for the filter's Optical Density (OD) of 0.6. The Optical Density is a logarithmic measure of the reduction in transmittance of a material. In this case, an OD of 0.6 means that the filter reduces the light intensity by a factor of 4 (or 63.1% transmittance).
The filter's geometry is that of a thin lens, and it is compatible with a wavelength of 300 nanometers. The item data also indicates that the filter has a "weblink status" of "Valid - in stock," suggesting that it is readily available for purchase.