This curve shows the attenuation as multiples of the 3dB bandwidth for filters with 2 to 10 sections. The importance of the combline style of filter is that it offers the systems designer an extremely low loss filter in the medium to wide bandwidth designs. A rough rule of thumb is 0.1dB per section.
Losses are even less for wider band filters.
Tapped holes on the bottom of the filter are normally provided for mounting purposes. The location and size of these holes is determined at the time of design.