Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020		Sep. 30, 2021	Sep. 30, 2020
Sales	$ 26,397,857	$ 21,277,797		$ 76,841,745	$ 65,135,959
Gross Profit	5,397,709	4,852,417		17,180,922	14,559,599
Operating Income	1,868,781	2,126,417		6,314,038	5,795,086
Pretax Income	1,491,400	1,904,421		6,754,815	4,981,413
Net Income	1,197,877	1,426,090		5,588,599	3,730,497
Commercial Air Handling [Member]
Sales	8,854,347	10,331,592	[1]	27,591,991	33,634,182	[1]
Gross Profit	1,420,320	2,488,067	[1]	5,681,179	8,429,409	[1]
Operating Income	291,729	1,350,939	[1]	2,182,452	4,536,190	[1]
Pretax Income	297,692	1,350,939	[1]	2,188,415	4,511,225	[1]
Net Income	223,269	1,013,204	[1]	1,641,311	3,383,419	[1]
Aerospace [Member]
Sales	17,543,510	10,946,205	[1]	49,249,754	31,501,777	[1]
Gross Profit	3,977,389	2,364,350	[1]	11,499,037	6,130,190	[1]
Operating Income	1,603,125	659,286	[1]	4,687,388	1,201,023	[1]
Pretax Income	1,734,115	455,643	[1]	4,417,620	422,555	[1]
Net Income	1,379,982	339,878	[1]	3,471,748	309,197	[1]
Industrial Hose [Member]
Sales		0	[1]	0	0	[1]
Gross Profit		0	[1]	706	0	[1]
Operating Income	(26,073)	116,192	[1]	(555,802)	57,873	[1]
Pretax Income	(540,407)	97,839	[1]	148,780	47,633	[1]
Net Income	(405,374)	73,008	[1]	475,540	37,881	[1]
Corporate and Other [Member]
Sales	26,397,857	21,277,797	[1]	76,841,745	65,135,959	[1]
Gross Profit	5,397,709	4,852,417	[1]	17,180,922	14,559,599	[1]
Operating Income	1,868,781	2,126,417	[1]	6,314,038	5,795,086	[1]
Pretax Income	1,491,400	1,904,421	[1]	6,754,815	4,981,413	[1]
Net Income	$ 1,197,877	$ 1,426,090	[1]	$ 5,588,599	$ 3,730,497	[1]

[1] Segment information for the three and nine month periods ended September 30, 2020 has been restated to reflect the change in reportable segments.