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Thank you for your answer heathfield. The link you suggested is very interesting although I have not yet had time to read it all. Page 23 is similar to what I wanted but those tests were for different reasons.
The reason I have in mind is (May be a silly question, like how long is a piece of string?) I want to have a dust extraction system to pick up the "dust" into a container.
The problem is if the filter medium is too coarse it lets through the dust. A finer medium rapidly clogs up and further suction is lost, with very little deposited in the container. Hence the question about partical size. But I suppose the size can go down infinitly small and therefore some will allways pass through the filter.
I need to have some size in mind in order to compare with the filter medium coupled with the fact that the finer the filter the quicker it be block.