This is a 33009FL01-290R Float Glass Plane Ruled Diffraction Grating, sourced from the reputable vendor MKS/Newport. The grating, which is 25 x 25 x 6 mm in dimension, is a Blazed Ruled Reflective Grating with a Sub Type of Rectangular.
The grating's physical data includes a blaze wavelength of 500, 1800 grooves, a blaze angle of 26.7 degrees, and an orientation vector of (1, 0, 0). The grating side is the front, and the order is 1. The material ID is soda lime ru clear, and the wavelength is 588.
The grating comes with a coating on the front side, specifically nwr 53-290r-2641-3-1. According to the vendor's website, the item is currently in stock and the weblink provided is valid.