Note 17 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Sales	$ 21,103,124	$ 22,244,681	$ 24,514,636	$ 21,836,087	$ 21,135,277	$ 19,771,137	$ 13,593,192	$ 11,878,700	$ 89,698,527	$ 66,378,306
Gross Profit	4,530,251	4,987,563	5,226,933	4,829,888	4,348,726	4,450,389	3,486,578	3,018,441	19,574,635	15,303,967
Operating Income	2,589,263	2,558,779	2,791,553	2,571,071	2,383,150	2,471,279	1,816,945	643,085	10,510,666	7,314,459
Pretax Income									9,419,490	5,281,730
Net Income	$ 1,708,058	$ 1,694,868	$ 1,831,479	$ 1,745,458	$ 1,348,254	$ 1,497,079	$ 394,625	$ 373,752	6,979,863	3,613,710
Commercial Air Handling [Member]
Sales									51,564,344	41,833,444
Gross Profit									12,350,412	11,046,113
Operating Income									7,141,097	6,409,687
Pretax Income									7,140,398	6,328,158
Net Income									5,291,035	4,746,119
Aerospace [Member]
Sales									30,126,438	14,397,557
Gross Profit									5,015,003	1,653,123
Operating Income									2,876,304	807,860
Pretax Income									2,073,239	630,966
Net Income									1,536,270	473,225
Industrial Hose [Member]
Sales									7,171,164	6,942,886
Gross Profit									1,970,149	1,813,752
Operating Income									859,114	820,881
Pretax Income									635,995	619,909
Net Income									471,272	464,461
Corporate and Other [Member]
Sales									836,581	3,204,419
Gross Profit									239,071	790,979
Operating Income									(365,849)	(723,969)
Pretax Income									(430,142)	(2,297,303)
Net Income									$ (318,714)	$ (2,070,095)