Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020
Sales	$ 26,449,885	$ 18,576,588		$ 50,443,889	$ 43,858,162
Gross Profit	5,780,290	3,499,039		11,783,211	9,707,182
Operating Income	2,119,797	530,520		4,445,257	3,668,669
Pretax Income	1,594,457	307,625		5,263,416	3,076,992
Net Income	1,247,305	228,837		4,390,722	2,304,407
Commercial Air Handling [Member]
Sales	9,972,545	11,848,816	[1]	18,737,644	23,302,590
Gross Profit	2,030,038	2,893,541	[1]	4,260,858	5,941,342
Operating Income	845,092	1,565,482	[1]	1,890,721	3,185,251
Pretax Income	845,092	1,565,482	[1]	1,890,721	3,160,286
Net Income	633,818	1,174,113	[1]	1,418,040	2,370,215
Aerospace [Member]
Sales	16,477,340	6,727,772	[1]	31,706,245	20,555,572
Gross Profit	3,750,252	605,498	[1]	7,522,353	3,765,841
Operating Income	1,342,966	(872,867)	[1]	3,094,411	541,737
Pretax Income	1,121,507	(1,154,315)	[1]	2,693,643	(33,088)
Net Income	893,184	(870,177)	[1]	2,099,368	(30,679)
Industrial Hose [Member]
Sales	0	0	[1]	0	0
Gross Profit	0	0	[1]	0	0
Operating Income	(68,261)	(162,095)	[1]	(539,875)	(58,319)
Pretax Income	(372,142)	(103,542)	[1]	679,052	(50,206)
Net Income	(279,697)	(75,099)	[1]	873,314	(35,129)
Corporate and Other [Member]
Sales	26,449,885	18,576,588	[1]	50,443,889	43,858,162
Gross Profit	5,780,290	3,499,039	[1]	11,783,211	9,707,182
Operating Income	2,119,797	530,520	[1]	4,445,257	3,668,669
Pretax Income	1,594,457	307,625	[1]	5,263,416	3,076,992
Net Income	$ 1,247,305	$ 228,837	[1]	$ 4,390,722	$ 2,304,407

[1] March 31, 2020 segment information has been restated to reflect the change in reportable segments.