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 6145-00-966-8961
NSN 5975-00-169-8918
NSN 5905-01-121-4264
NSN 6645-01-616-7897
NSN 6135-01-507-4346
NSN 6320-00-394-8458
NSN 5910-01-408-0630
NSN 7035-01-431-1448
NSN 5960-01-008-8902
NSN 5985-01-514-3575
NSN 5990-01-306-9290
NSN 2925-01-342-1712