Using life: The properties of the range do not deteriorate even after a long timein stock, as long as they are maintained in their original packaging.Transport: The original packaging is recommended.Dimensions: The filter lens shall be of such dimensions as to fit suitably into the frame and to cover the window, to prevent leakage of radiations. The filter lens shall be no less than 2mm nor more than 3.8mm tolerance of dimension of ± 0.1mm and ±0.8mm wide and lengthOptical Qualities- cover lens, filter lens,safety plateBoth surfaces, waves or other defects that would impair their optical quality lens surfaces shall be flat and substantially parallel, prismatic effects shall not exceed 1/8 prism diopter (approximately 4.3 minutes of angular deviation)