Note 17 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Sales	$ 19,933,941	$ 21,277,797	$ 18,576,588	$ 25,281,574	$ 21,103,124	$ 22,244,681	$ 24,514,636	$ 21,836,087	$ 85,069,900	$ 89,698,527
Gross Profit	4,371,691	4,852,417	3,499,039	6,208,143	4,530,251	4,987,563	5,226,933	4,829,888	18,931,290	19,574,635
Operating Income	1,657,368	2,126,417	530,520	3,138,149	2,589,263	2,558,779	2,791,553	2,571,071	7,452,453	10,510,666
Pretax Income									7,475,241	9,419,490
Net Income	$ 2,108,890	$ 1,426,090	$ 228,837	$ 2,075,570	$ 1,708,058	$ 1,694,868	$ 1,831,479	$ 1,745,458	5,839,387	6,979,863
Commercial Air Handling [Member]
Sales									41,243,413	51,564,344
Gross Profit									10,216,587	12,350,412
Operating Income									5,313,487	7,141,097
Pretax Income									5,750,226	7,140,398
Net Income									4,312,669	5,291,035
Aerospace [Member]
Sales									18,916,525	30,126,438
Gross Profit									1,415,591	5,015,003
Operating Income									(649,230)	2,876,304
Pretax Income									(1,164,179)	2,073,239
Net Income									(873,134)	1,536,270
Industrial Hose [Member]
Sales									22,762,199	7,171,164
Gross Profit									6,518,682	1,970,149
Operating Income									3,746,257	859,114
Pretax Income									2,114,580	635,995
Net Income									1,585,935	471,272
Corporate and Other [Member]
Sales									2,147,763	836,581
Gross Profit									780,430	239,071
Operating Income									(958,061)	(365,849)
Pretax Income									774,614	(430,142)
Net Income									$ 813,917	$ (318,714)