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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, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Net Sales $ 4,641,483 $ 9,297,186 $ 14,923,327 $ 16,718,384
Liquid Filters [Member]        
Net Sales 2,551,710 8,453,136 10,531,998 13,493,469
Ceramic Diesel Particulate [Member]        
Net Sales 1,160,695 747,234 2,720,757 2,990,502
Plastic Products [Member]        
Net Sales 762,384 0 1,343,794 0
Development Projects [Member]        
Net Sales $ 166,694 $ 96,815 $ 326,778 $ 234,413