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 grating substrate.

Grating size - 55 x 55 mm
Focal length - infinity
Grooves / mm - 1200
Blaze angle - 17 degrees, 27 minutes
Catalog number 35-53-06-280
Part number 43-5-10
Coating - Al (?)

There are some chips in the grating along one edge (see second photo) and a very fine scratch near the margin, but otherwise the grating appears to be in excellent condition. There is no holder included. Plastic protective cover is present.

Photo set 1654