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Note 1 - Summary of Significant Accounting Policies - Sales by Product Line (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Net Sales $ 22,526,201 $ 32,637,484
Liquid Filters [Member]    
Net Sales 14,147,842 25,464,614
Ceramic Diesel Particulate [Member]    
Net Sales 5,131,891 5,652,686
Plastic Products [Member]    
Net Sales 2,647,366 895,203
Development Projects [Member]    
Net Sales $ 599,102 $ 625,981