Here is a 27mm diameter PL (polarizing) filter, which can be hard to find. It can be attached to lenses with a 27mm diameter. For example, if you have a monocular with a 27mm diameter, attaching this filter could increase contrast and make viewing easier. There are no markings. It can be used in various ways, such as reducing glare and enhancing the contrast of landscapes. It has some signs of use, but it's still quite clean. The filter rotates smoothly after being attached. If you're looking for one, please consider it.