Note 12 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Sales	$ 18,576,588	$ 24,514,636	$ 43,858,162	$ 46,350,723
Gross Profit	3,499,039	5,226,933	9,707,182	10,056,821
Operating Income	530,520	2,791,553	3,668,669	5,362,624
Pretax Income	307,625	2,481,439	3,076,992	4,810,311
Net Income	228,837	1,831,479	2,304,407	3,576,937
Commercial Air Handling [Member]
Sales	11,848,816	14,880,504	23,302,590	26,625,065
Gross Profit	2,893,541	3,549,109	5,941,342	6,551,042
Operating Income	1,565,482	2,244,680	3,185,251	4,027,667
Pretax Income	1,565,482	2,244,481	3,160,286	4,027,177
Net Income	1,174,113	1,683,361	2,370,215	3,020,384
Aerospace [Member]
Sales	2,587,421	7,457,377	9,843,247	15,477,780
Gross Profit	(499,569)	1,038,395	771,191	2,295,400
Operating Income	(991,953)	414,464	(251,705)	1,174,074
Pretax Income	(1,134,193)	231,296	(548,265)	794,253
Net Income	(850,645)	169,377	(411,199)	593,097
Industrial Hose [Member]
Sales	4,046,814	1,933,725	10,296,535	3,730,816
Gross Profit	1,088,811	592,245	2,851,178	1,117,979
Operating Income	227,498	295,701	893,081	543,989
Pretax Income	88,290	214,536	614,816	407,013
Net Income	62,082	159,385	455,552	302,456
Corporate and Other [Member]
Sales	93,537	243,030	415,790	517,062
Gross Profit	16,256	47,184	143,471	92,400
Operating Income	(270,507)	(163,292)	(157,958)	(383,106)
Pretax Income	(211,954)	(208,874)	(149,845)	(418,132)
Net Income	$ (156,713)	$ (180,644)	$ (110,161)	$ (339,000)