A flat, transparent piece of glass, generally of fused quartz, with one or both principal surfaces polished to within a few millionths of an inch of a true plane. It is used in conjunction with a monochromatic light source to measure the flatness of precision finished surfaces, and to determine the distance and parallelism between precision finished surfaces by comparison with known standards. In operation the flat is superimposed, reference surface downward, on the parts under test and when illuminated by monochromatic light the rays reflected from the reference surface are either reinforced or neutralized by the rays reflected from the surface under test producing interference bands which reveal any variations in the thickness of the film of air between surface under test and the flat. Excludes optical parallels.
NSN 6610-01-271-1205
NSN 6130-01-004-8977
NSN 6135-01-204-8712
NSN 6105-01-182-2767
NSN 6645-01-105-9107
NSN 5996-01-225-2829
NSN 5930-00-602-4531
NSN 4140-01-386-9821
NSN 5965-01-075-3148
NSN 5915-00-063-3689
NSN 5960-00-067-0038
NSN 5930-00-133-5685