This is very affordable, unmounted, 1 inch (25.4mm) diameter optical slit, made of aluminium.
The front side is marked with slit length and width, the back side is left blank. The thin middle line marked on the front side helps with the alignment.
Width tolerance: +0/-5um
Thickness: 0.2mm (standard) or 0.1mm (special)
If required, the area where the slit is located can be further thinned out by laser etching down to ca. 0.1mm thickness. This is in most applications not required but can be done for a higher price (see options next to product photo).
Great for DIY spectrometers, slit-scan imaging, image- and laser beam sampling or other optical experiments.