Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended			12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020		Dec. 31, 2020
Sales	$ 23,994,004	$ 25,281,574
Gross Profit	6,002,921	6,208,143
Operating Income	2,325,460	3,138,149
Pretax Income	3,668,959	2,769,367
Net Income	3,143,417	2,075,570		$ 5,839,387
Commercial Air Handling [Member]
Sales	8,765,099	11,453,774	[1]
Gross Profit	2,230,821	3,047,801	[1]
Operating Income	1,045,631	1,619,769	[1]
Pretax Income	1,045,631	1,594,804	[1]
Net Income	784,224	1,196,102	[1]
Aerospace [Member]
Sales	15,228,905	13,827,800	[1]
Gross Profit	3,772,100	3,160,342	[1]
Operating Income	1,751,443	1,414,604	[1]
Pretax Income	3,025,970	1,121,227	[1]
Net Income	2,660,019	839,496	[1]
Industrial Hose [Member]
Sales			[1]
Gross Profit			[1]
Operating Income	(471,614)	103,776	[1]
Pretax Income	(402,642)	53,336	[1]
Net Income	(300,826)	39,972	[1]
Corporate and Other [Member]
Sales	23,994,004	25,281,574	[1]
Gross Profit	6,002,921	6,208,143	[1]
Operating Income	2,325,460	3,138,149	[1]
Pretax Income	3,668,959	2,769,367	[1]
Net Income	$ 3,143,417	$ 2,075,570	[1]

[1] March 31, 2020 segment information has been restated to reflect the change in reportable segments.