19. SELECTED QUARTERLY CONSOLIDATED FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2020	May 31, 2019	May 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 3,773	$ 6,111	$ 6,874	$ 5,533	$ 7,242	$ 3,163	$ 5,911	$ 4,740	$ 22,291	$ 21,056	$ 29,555
Gross profit (loss)	(93)	2,991	3,202	2,271	3,379	272	2,398	1,553	8,371	7,602	12,386
Net (loss) income	$ (2,885)	$ 245	$ 251	$ (413)	$ 110	$ (3,201)	$ (629)	$ (1,515)	$ (2,802)	$ (5,235)	$ 528
Net (loss) income per share basic and diluted	$ (.13)	$ .01	$ .01	$ (.02)	$ 0.00	$ (0.14)	$ (0.03)	$ (0.07)	$ (0.12)	$ (0.23)	$ 0.02