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Note 1 - Summary of Significant Accounting Policies - Sales by Product Line (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Revenue $ 4,016,563 $ 4,641,483 $ 8,014,440 $ 14,923,327
Liquid Filters [Member]        
Revenue 1,080,004 2,551,710 2,237,340 10,531,998
Diesel Particulate Filters [Member]        
Revenue 1,810,743 1,160,695 3,741,807 2,720,757
Plastic Products [Member]        
Revenue 1,016,370 762,384 1,830,396 1,343,794
Development Projects [Member]        
Revenue $ 109,446 $ 166,694 $ 204,897 $ 326,778