A large certified precision ruled diffraction grating by Bausch & Lomb of Rochester, New York.

600 grooves / mm
Blaze angle 28 degrees, 41 minutes.
Radius concave

Serial number: 889-8-1-3
Catalogue number 35 53 12 55

Width: 20 cm.

Depth: 8 cm.

Height: 17.5 cm.

(window: 10 x 13.5 cm).

2.16 kgs.

For a similar diffraction grating by Bausch and Lomb see the collection of the Smithsonian National Air and Space Museum. Inventory Number: A19980111000

https://airandspace.si.edu/collection-objects/diffraction-grating-prime-focus-spectrograph/nasm_A19980111000