This is a borosilicate hand ground focusing screen with clipped corners. It measures exactly 4x5" and is 2.0mm thick. It will fit just about any camera requiring an exactly 4x5" screen with clipped corners. Square corners are available upon request.
Borosilicate glass is harder, stronger and more durable than regular soda-lime glass. This makes it better for defending from scratches and breakage.
And, importantly it is brighter too! This screen is ground for brightness. It is made with the finest/highest grade of grit possible to allow for a very fine diffusion. In camera, you can see the details in highlights and shadows, but depending on aperture, the lens may be visible and distracting through the ground glass. That just comes with the territory of ultra bright ground glass. This screen is designed for the more advanced photographer who desires the best and brightest view.
Borosilicate lacks the blue green color of soda-lime glass. It is almost colorless, but bigger pieces will display a slight yellow color when edge viewed.
Borosilicate is hard to cut and work. It has a tendency to not score right and to snap evenly. Consequently there can be a lot of waste and lost time when making screens. This glass is much more expensive to buy for stock which is reflected in my pricing. But, if you want the best and brightest go with borosilicate!