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Note 1 - Summary of Significant Accounting Policies - Sales by Product Line (Details) - USD ($)
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Net Sales $ 10,281,844 $ 7,421,198
Ceramic Diesel Particulate [Member]    
Net Sales 1,560,062 2,243,268
Liquid Filters [Member]    
Net Sales 7,980,287 5,040,333
Plastic Products [Member]    
Net Sales 581,411
Development Projects [Member]    
Net Sales $ 160,084 $ 137,597