Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Sales	$ 22,244,681	$ 19,771,137	$ 68,595,404	$ 45,243,029
Gross profit	4,987,563	4,450,222	15,044,384	10,955,241
Operating income	2,558,779	2,471,279	7,921,403	4,931,309
Income (loss) before provision for income taxes	2,236,782	2,087,183	7,047,093	3,111,685
Income (loss) before provision for income taxes	2,236,782	2,087,183	7,047,093	3,111,685
Operating Segments [Member] | Commercial Air Handling [Member]
Sales	12,878,988	9,876,700	39,504,053	29,876,961
Gross profit	2,915,767	2,743,833	9,466,810	7,861,725
Operating income	1,509,077	1,696,934	5,536,745	4,357,970
Income (loss) before provision for income taxes	1,508,944	1,686,296	5,536,122	4,316,875
Income (loss) before provision for income taxes	1,508,944	1,686,296	5,536,122	4,316,875
Operating Segments [Member] | Test and Measurement [Member]
Sales	29,893	790,297	532,076	2,786,742
Gross profit	4,933	130,293	87,792	722,062
Operating income	4,933	130,293	87,792	(239,151)
Income (loss) before provision for income taxes	4,933	130,293	87,792	(94,828)
Income (loss) before provision for income taxes	4,933	130,293	87,792	(94,828)
Operating Segments [Member] | Industrial Hose [Member]
Sales	1,823,950	1,718,138	5,554,766	5,193,324
Gross profit	403,158	356,000	1,521,137	1,151,358
Operating income	137,640	111,419	681,628	413,573
Income (loss) before provision for income taxes	69,697	48,454	476,710	272,608
Income (loss) before provision for income taxes	69,697	48,454	476,710	272,608
Operating Segments [Member] | Aerospace [Member]
Sales	7,386,930	7,386,002	22,864,710	7,386,002
Gross profit	1,611,655	1,220,096	3,907,056	1,220,096
Operating income	1,073,388	706,424	2,247,461	706,424
Income (loss) before provision for income taxes	830,865	620,023	1,625,116	620,023
Income (loss) before provision for income taxes	830,865	620,023	1,625,116	620,023
Corporate, Non-Segment [Member]
Sales	124,920		139,799
Gross profit	52,050		61,589
Operating income	(166,259)	(173,791)	(632,223)	(307,507)
Income (loss) before provision for income taxes	(177,657)	(397,883)	(678,647)	(842,419)
Income (loss) before provision for income taxes	(177,657)	(397,883)	(678,647)	(842,419)
Consolidation, Eliminations [Member]
Income (loss) before provision for income taxes				(1,160,574)
Income (loss) before provision for income taxes				$ (1,160,574)