Carbon Steel Bolt Grade Markings

Head markings for popular grades of carbon steel externally threaded fasteners

Grade Identification Marking	Specification	Material	Nominal Size  (inch)	Proof Load Stress  (ksi)	Tensile Strength  (min ksi)	Rockwell Hardness  (min)	Rockwell Hardness  (max)	See Note
	SAE J429 - Grade 2	Low or Medium Carbon Steel	1/4 thru 3/4	55	74	B80	B100	-
			over 3/4 thru 1-1/2	33	60	B70	B100	-
	ASTM A307 - Grade A	Low or Medium Carbon Steel	1/4 thru 4	-	60	B69	B100	-
	ASTM A307 - Grade B	Low or Medium Carbon Steel	1/4 thru 4	-	60 min 100 max	B69	B95	-
	SAE J429 - Grade 5	Medium Carbon Steel, Quenched and Tempered	1/4 thru 1	85	120	C25	C34	-
	ASTM A449 - Type 1	Medium Carbon Steel, Quenched and Tempered	over 1 thru 1-1/2	74	105	C19	C30	-
			over 1-1/2 thru 3	55	90	183	235	3
	ASTM A325 - Type 1	Medium Carbon Steel, Quenched and Tempered	1/2 thru 1	85	120	C24	C35	4
			over 1 to 1-1/2	74	105	C19	C31	4
	ASTM A325 - Type 3	Atmospheric Corrosion Resistant  Steel, Quenched and Tempered	1/2 thru 1	85	120	C24	C35	5
			over 1 to 1-1/2	74	105	C19	C31	5
	ASTM A354 - Grade BC	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 thru 2-1/2	105	125	C26	C36	-
			over 2-1/2  thru 4	95	115	C22	C33	-
	SAE J429 - Grade 8	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 thru 1-1/2	120	150	C33	C39	-
	ASTM A354 - Grade BD	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 thru 2-1/2	120	150	C33	C39	6
			over 2-1/2  thru 4	105	140	C31	C39	6
	ASTM A490 - Type 1	Medium Carbon Alloy Steel, Quenched and Tempered	1/2 thru 1-1/2	120	150 min 170 max	C33	C38	-
	ASTM A490 - Type 3	Atmospheric Corrosion Resistant  Steel, Quenched and Tempered	1/2 thru 1-1/2	120	150 min 170 max	C33	C38	5

NOTES:

1. In addition to the the indicated grade marking, all grades included in this table must be marked for manufacturer identification.
   
   
2. While hex heads are shown, grade markings apply equally to products with other head configurations.
   
   
3. Brinell hardness numbers are shown for A490 Type 1 bolts over 1-1/2 inch thru 3 inch.
   
   
4. A325 Type 1 bolts may also be marked with 3 radial lines 120° apart in addition to the A325 marking.
   
   
5. The bolt manufacturer, at his option, may add other markings to indicate the use of atmospheric corrosion resistant material.
   
   
6. A354 Grade BD products, in sizes 1-1/2 inch and smaller, are identified as shown and, at the manufacturer's option, may have the letters BD added. Larger sizes are marked only by BD.