>ASTM A320 material was originally approved in 1948. This Standard is normally used in the petrol field and in chemical products applications. The ASTM Standard covers the steel and stainless steel alloys suitable for the fastening of low working temperature materials, it also includes the specifications of fastening devices to be used in pressure vessels, valves, flanges and fittings.

Here following is a basic summary of few common grades. ASTM A320 also includes further standard specifications, not listed in this summary including B5, B6 and B16.

L7 Alloy steel, AISI 4140/4142 Quenched and tempered

L43 Alloy steel, AISI 4340 Quenched and tempered

B8 Class 1 Stainless steel, AISI 304, carbide solution treated

B8M Class 1 Stainless steel, AISI 316, carbide solution treated

B8 Class 2 Stainless steel, AISI 304, carbide solution treated, strain hardened

B8M Class 2 Stainless steel, AISI 316, carbide solution treated, strain hardened

»ASTM A320 RECOMMENDED NUTS and WASHERS

Grade	Size	Tensile, ksi, min	Yield, ksi, min	Charpy Impact 20-ft-lbf @ temp	Elong, %, min.	RA, %, min
ASTM A320 L7	up to 21/2	125	105	-150° F	16	50
ASTM A320  L43	sup a 4	125	105	-150° F	16	50
ASTM A320  B8 Class 1	all	75	30	N/A	30	50
ASTM A320 B8M Class 1	all	75	30	N/A	30	50
ASTM A320 B8 Class 2	Up to 3/4	125	100	N/A	12	35
	7/8 - 1	115	80	N/A	15	35
	11/8 - 11/4	105	65	N/A	20	35
	13/8 - 11/2	100	50	N/A	28	45
ASTM A320 B8M Class 2	Up to 3/4	110	95	N/A	15	45
	7/8 - 2001	100	80	N/A	20	45
	11/8 - 11/4	95	65	N/A	25	45
	13/8 - 11/2	90	50	N/A	30	45

» MECHANICAL PROPERTIES

Grade	Nuts	Washers
ASTM A320 L7	A194 Grade 4 o 7	F436
ASTM A320 L43	A194 Grade 4 o 7	F436
ASTM A320 B8 Class 1	A194 Grade 8	SS304
ASTM A320 B8M Class 1	A194 Grade 8M	SS316
ASTM A320 B8 Class 2	A194 Grade 8 Grade 80	SS304
ASTM A320 B8M Class 2	A194 Grade 8M  Grade 80	SS316