A4-50 Stainless Steel Fastener is recognized by 2 ways, A2 which describe it as being from SS 316 family and 50 which classifies its strength. When we say A4-50 it generally means that the bolt / screw is from SS 316 grade and has an ultimate tensile strength as 50 kg or 500 n/mm2.

A4-50

Hex bolts, screws, stud bolts, double ended studs, full thread rods, full threaded studs

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	TensileStrengthRma min. Mpa	Stress at 0.2 % permanent strain Rp0.2a min. Mpa	Elongation after fracture Ab min. mm
Austenitic	A1, A2	50	500	210	0.6d
	A3, A4	70	700	450	0.4d
	A5	80	800	600	0.3d