ISO 3506-2 specifies the mechanical and chemical properties for hexagon nut in grade A4-50 and made of austenitic and ferritic steel grades of corrosion resistance stainless steel grade. This standard and its part mainly pertains to hexagon nuts with nominal diameter up to M-39 or 39 mm.

A4-50 means that A4 which stands for series 316 material and 50 which means the strength of the hexagon nut.

A4-50

Hex Nuts, Jam Nut, Lock Nut & Thin Nuts

Steel Group	Steel Grade	Chemical composition
		mass fraction, % (maxima unless stated))
		C	Si	Mn	P	S	Cr	Mo	Ni	Cu
Austenitic	A1	0.12	1	6.5	0.2	0.15 to 0.35	16 to 19	0.7	5 to 10	1.75 to 2.25
	A2	0.10	1	2	0.05	0.03	15 to 20	-	8 to 19	4
	A3	0.08	1	2	0.045	0.03	17 to 19	-	9 to 12	1
	A4	0.08	1	2	0.045	0.03	16 to 18.5	2 to 3	10 to 15	4
	A5	0.08	1	2	0.045	0.03	16 to 18.5	2 to 3	10.5 to 14	1

Steel Group	Steel Grade	Property Class		Stress Under proof load Sp min. MPA
		Nuts with m ≥ 0.8d	Nuts with 0.5d ≤ m < 0.8d	Nuts with m ≥ 0.8d	Nuts with 0.5d ≤ m < 0.8d
Austenitic	A1, A2	50	025	500	250
	A3, A4	70	035	700	350
	A5	80	040	800	400