Special Features:

Glass is mirror selec (for silvering) ; element per mil-r-6771, type i; clear aperature = entrance 66 mm x 63.5mm; surface quality = central zone 30-10, outer zone 40-20 per mil-o-13830; light deviation not to exceed 2 min. Ofarc; angle of incidence = 45 deg., white light reflectance 40% +/- 5%, absorption not to exceed 5%; edge chips allowable outside central zone, size and number per mil-o-13830; all edges chamfered to 0.01 + x 45 deg. +/- 5 deg. ; part to be handled on edges only; 2 corners on polished sides chamfered to0.030 in. X 45 deg.; opposite 2 corners are chamfered to 0.480 in. X 44 degrees

Properties:

A transparent item of a predetermined size that permits unobstructed and undistorted view of a desired area. It may include a frame, have reference markings, grid lines and may be heat strengthened and/or tinted. It is generally used where safety, security, and/or the restriction of foreign matter are required, such as the visual examination of the inside of pressurized tanks, liquid sights, controlled liquid flow, and inspection of equipment enclosed in a housing. See window (as modified); scale, cathode ray tube; scale, plotting; window, metal; window, wood; and window panel, aircraft.