Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Sales	$ 24,514,636	$ 13,593,192	$ 46,350,723	$ 25,471,892
Gross profit	5,226,933	3,486,578	10,056,821	6,505,019
Operating income	2,791,553	1,816,945	5,362,624	2,460,030
Income (loss) before provision for income taxes	2,481,439	526,166	4,810,311	1,024,502
Operating Segments [Member] | Commercial Air Handling [Member]
Sales	14,880,504	10,884,324	26,625,065	20,000,261
Gross profit	3,549,109	2,970,767	6,551,042	5,117,892
Operating income	2,244,680	1,780,930	4,027,667	2,661,036
Income (loss) before provision for income taxes	2,244,481	1,765,374	4,027,177	2,630,579
Operating Segments [Member] | Test and Measurement [Member]
Sales	228,152	924,598	502,184	1,996,445
Gross profit	37,645	116,743	82,861	591,769
Operating income	37,645	(259,273)	82,861	(369,304)
Income (loss) before provision for income taxes	37,645	(374,025)	82,861	(502,974)
Operating Segments [Member] | Industrial Hose [Member]
Sales	1,933,725	1,784,270	3,730,816	3,475,186
Gross profit	592,245	399,068	1,117,979	795,358
Operating income	295,701	162,141	543,989	302,153
Income (loss) before provision for income taxes	214,535	123,964	407,013	224,153
Operating Segments [Member] | Aerospace [Member]
Sales	7,457,377		15,477,780
Gross profit	1,038,395		2,295,400
Operating income	414,464		1,174,074
Income (loss) before provision for income taxes	231,296		794,253
Corporate, Non-Segment [Member]
Sales	14,878		14,878
Gross profit	9,539		9,539
Operating income	(200,937)	133,147	(465,967)	(133,855)
Income (loss) before provision for income taxes	$ (246,518)	$ (989,147)	$ (500,993)	$ (1,327,256)