This is a certified precision Bausch & Lomb optical grating. Much of the following information was taken from the nomenclature label fixed to the back of the rear cover. Because this is a transmission grating, it includes covers for both the front and rear sides.

Grating size - 110 x 110 mm (102mm ruled area)
Focal length - infinity
Grooves / mm - 600
Blaze angle - 28 degrees 41 minutes
Catalog number - 35-53-63-55
Serial number - 570-22-7-8
Coating - none

This grating is evidently unused with the original Bausch & Lomb sealing tape applied to both the front and rear protective covers. No blemishes were apparent through the protective covers which have not been disturbed.

Photo set 1661