Note 12 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Sales	$ 25,281,574	$ 21,836,087
Gross Profit	6,208,143	4,829,888
Operating Income	3,138,149	2,571,071
Pretax Income	2,769,367	2,328,872
Net Income	2,075,570	1,745,458	$ 6,979,863
Commercial Air Handling [Member]
Sales	11,453,774	11,744,561
Gross Profit	3,047,801	3,001,933
Operating Income	1,619,769	1,782,987
Pretax Income	1,594,804	1,782,696
Net Income	1,196,102	1,337,022
Aerospace [Member]
Sales	7,255,826	8,020,403
Gross Profit	1,270,760	1,257,006
Operating Income	740,248	759,609
Pretax Income	585,928	562,956
Net Income	439,446	423,718
Industrial Hose [Member]
Sales	6,249,721	1,797,091
Gross Profit	1,762,367	525,735
Operating Income	665,583	248,291
Pretax Income	526,526	192,479
Net Income	393,470	143,073
Corporate and Other [Member]
Sales	322,253	274,032
Gross Profit	127,215	45,214
Operating Income	112,549	(219,816)
Pretax Income	62,109	(209,259)
Net Income	$ 46,552	$ (158,355)