Polarizing filter # 3, transmitting approximately 50% of light. The combination of two filters # 3 allows you to adjust the transmission in the range of 50-1%. Both a single filter and two combined polarizing filters # 3 are used in all telescopes, also large ones. It allows for optimal transmission conditions. and also when you want to combine color or specialist filters (SkyGlow, Contrast Booster, Semi-APO) with a filter that reduces transmission.
The filter is screwed into 1.25 inch glasses equipped with a filter thread or equipped with filter thread sleeves, angular connectors, Barlow lens.

(below: two polarizing filters connected)

Question : How does a single polarizing filter work? Why do you need two filters in the set? What is the physical basis of the operation of such a filter?

Answer: The light of the moon and planets is a non-polar light. The polarizing filter "cuts out" the electromagnetic wave components with a specific polarization. Two polarizing filters can therefore "cut" almost all light on non-falling, and the transmission is regulated by the rotation of one filter against the other. For people who always want to understand exactly, we recommend an article about the polarization of light on Wikipedia (note: in English) .

Question : How do you fix the eyepiece filter?

Answer: The filter is screwed into the eyepiece from the side of the extractor, ie from the opposite side than the eye. The offered set is used with 1.25 "glasses. Among the currently offered eyeglasses there are no eyeglasses without a filter thread, so you can say that the set of polarizing filters can be used with EVERY 1,25" eyepiece.