Special Features:

Fram (body) consists of 3/4-14 aluminum straight pipe; window includes: frame, 3 neoprene spacer washers, 2 aluminum nuts, 1 rubber o-ring and a clear plastic viewer window; dimensions including frame: 1.380 inch in diameter by 0.630 inch thick; cage calls this: sight glass

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.