Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Sales	$ 21,277,797	$ 22,244,681	$ 65,135,959	$ 68,595,404
Gross Profit	4,852,417	4,987,563	14,559,599	15,044,384
Operating Income	2,126,417	2,558,779	5,795,086	7,921,403
Pretax Income	1,904,421	2,236,782	4,981,413	7,047,093
Net Income	1,426,090	1,694,868	3,730,497	5,271,805
Commercial Air Handling [Member]
Sales	10,331,592	12,878,988	33,634,182	39,504,053
Gross Profit	2,488,067	2,915,768	8,429,409	9,466,810
Operating Income	1,350,939	1,509,078	4,536,190	5,536,744
Pretax Income	1,350,939	1,508,945	4,511,225	5,536,121
Net Income	1,013,204	1,131,709	3,383,419	4,152,092
Aerospace [Member]
Sales	4,468,253	7,386,930	14,311,500	22,864,710
Gross Profit	389,624	1,611,656	1,160,815	3,907,056
Operating Income	(146,903)	1,073,389	(398,608)	2,247,461
Pretax Income	(254,600)	830,866	(802,865)	1,625,117
Net Income	(190,950)	623,151	(602,149)	1,216,260
Industrial Hose [Member]
Sales	6,137,905	1,823,950	16,434,440	5,554,766
Gross Profit	1,842,287	403,158	4,693,465	1,521,137
Operating Income	860,076	137,640	1,753,157	681,632
Pretax Income	764,130	69,698	1,378,946	476,711
Net Income	571,747	50,135	1,027,299	352,593
Corporate and Other [Member]
Sales	340,047	154,813	755,837	671,875
Gross Profit	132,439	56,981	275,910	149,381
Operating Income	62,305	(161,328)	(95,653)	(544,434)
Pretax Income	43,952	(172,727)	(105,893)	(590,856)
Net Income	$ 32,089	$ (110,127)	$ (78,072)	$ (449,140)