stainless - 304 vs f593c article

Marking Stainless Fasteners

Industrial Fasteners Institute • 636 Oak Tree Blvd. • Independence Ohio 44131-2500Phone: 216-241-1482 • Fax: 216-241-5901 • www.indfast.org

By Joe Greenslade, Director of Engineering Technology, IFI

e sure when filling a purchaser’s order for stain-less steel bolts and/or nuts that they are pro-

vided exactly what they ask for. Many stainless steelbolts and nuts are simply marked “304” or “316”. Thesemarkings do not indicate compliance with any particu-lar industrial standard. They do not assure the pur-chaser of any chemistry, strength, or performance char-acteristics as are spelled out in the ASTM standards.The markings imply that the chemistry meets the re-quirements of the UNS S30400 or S31600 material,but that is not assured or mandated by any standardsbody like SAE, ASME, or ASTM. Bolts and nutsmarked in this way may meet all of the requirementsof one or more of the ASTM standards, but since these

B

Not All Stainless Bolt and Nut MarkingsAssure Conformance to Standards

No StandardNo Requirements

ASTM F593Defined Requirements

are not the markings required by ASTM there is noindication or assurance of such compliance.

If a purchaser just states, “I want 18-8 bolts andnuts.” Or “I want 304 stainless bolts and nuts.” Thenthose marked simply “304” are probably suitable. If thepurchaser makes any reference to ASTM fastenersmarked “304” or “316” are not suitable because theyare not properly marked to comply with ASTM stan-dards.

To assure purchasers they have stainless steel fas-teners that will provide specific chemistry and physi-cal characteristics, either ASTM A193 or ASTM A593should be specified for bolts and either ASTM A194 orASTM A594 should be specified for nuts. Below is atable that shows the difference between specifying anASTM standard verses fasteners simply marked “304”or “316”.

In addition to grade marking, ASTM requires boltsand nuts to be marked with a manufacturer’s identifi-cation mark.

If stainless steel bolts and nuts are requested be-cause they are intended to meet specific[JV2] appli-cation requirements, they should be specified by us-ing an appropriate standard reference. This is the onlyway to assure that the desired performance will be pro-vided by the fasteners. It is good practice to specifyfasteners that are marked and verified as meeting aspecific ASTM standard instead of requesting fasten-

Marking

304

B8

B8A

F593C

F593D

316

B8M

B8MA

F593G

F593H

Standard

None

ASTM A193

ASTM A193

ASTM F593 1/4 thru 5/8

ASTM F593 3/4 thru 1-1/2

None

ASTM A193

ASTM A193

ASTM F593 1/4 thru 5/8

ASTM F593 3/4 thru 1-1/2

Chemistry

None

Type 304 stainless steel




None





Tensile Strength

None

75 ksi min.

75 ksi min.

100 - 10 ksi

85 - 140 ksi

None

75 ksi min.

75 ksi min.

100 - 10 ksi

85 - 140 ksi

Yield Strength

None

30 ksi min.

30 ksi min.

65 ksi min.

45 ksi min.

None

30 ksi min.

30 ksi min.

65 ksi min.

45 ksi min.

Hardness

None

HRB 96 max.

HRB 90 max.

HRB 90 - HRC 32

HRB 85 - HRC 32

None

HRB 96 max.

HRB 90 max.

HRB 90 - HRC 32

HRB 85 - HRC 32

Bolts

IFI-Greenslade.pmd 7/8/2011, 9:35 AM1

Marking

304

8

8A

F594C

F594D

316

8 M

8MA

F594G

F594H

Standard

None

ASTM A194

ASTM A194

ASTM F594

ASTM F594

None

ASTM A194

ASTM A194

ASTM A594

ASTM F594

Chemistry

None





None





Proof Load

None

Heavy Hex, 80 ksi Hex, 75 ksi

Heavy hex, 80 ksi Hex, 75 ksi

100 ksi

85 ksi

None



100 ksi

85 ksi

Hardness

None

HRB 60 - 105

HRB 60 - 90

HRB 95 - HRC 32

HRB 80 - HRC 32

None

HRB 60 - 105

HRB 60 - 90

HRB 95 - HRC 32

HRB 80 - HRC 32

Nuts

ers referring to the parts by slang or generic termsonly, such as “18-8”, “304” or “316”.

For more information about the proper use of fas-tener standards send questions to the author at

[email protected] or subscribe to the state-of-the-art online technical support service, IFI TechnologyConnection, at www.indfast.org,

IFI-Greenslade.pmd 7/8/2011, 9:35 AM2

stainless - 304 vs f593c article

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