A194 nuts · ASTM A194 / ASME SA-194

ASTM A194 Grade 8M (316 Stainless)

316 stainless heavy hex nut for B8M studs — molybdenum-bearing for chloride and marine service, 80 ksi proof load.

UNS S31600Alloy AISI 316Type Austenitic molybdenum-bearing stainless steel nut, forged or machined from bar (A type solution treated after finishing)

Overview Chemistry Mechanical Standards Products Applications Guide

Material overview

What A194 8M is.

ASTM A194 Grade 8M is the 316 stainless nut that completes an A193 or A320 B8M stud bolt set. Molybdenum gives it the pitting and crevice-corrosion resistance the 304-based Grade 8 lacks, so it is the nut for offshore, coastal, seawater and chemical flanges.

It is solution treated, proof-load rated at 80 ksi and hardness limited to 300 HBW. We machine 8M nuts from certified 316 and 316L bar, with silver plating, PTFE coating or oversize tapping available to control galling.

Get a Quote Download the A194 8M data sheet (PDF)

Proof load stress80 ksi heavy hex · 75 ksi hex

Hardness126–300 HBW

Heat treatmentNone required; 8MA type is solution treated after finishing

PatternHeavy hex (ASME B18.2.2)

Companion studASTM A193 / A320 B8M

Typical service−425 °F to 1500 °F

Nominal composition

Fe balance ≈ 66.9%Cr ≈ 17.00%Ni ≈ 12.00%Mo ≈ 2.50%Mn ≈ 1.00%Si ≈ 0.50%C, P, S trace

Midpoints of the specification ranges, for orientation only. Limits are in the table below.

Specifications & technical data

Chemical composition.

Download the data sheet (PDF) →

Chemical composition — ASTM A194 Grade 8M (AISI 316, UNS S31600)

Element	Symbol	Min %	Max %
Carbon	C	—	0.08
Manganese	Mn	—	2.00
Phosphorus	P	—	0.045
Sulfur	S	—	0.030
Silicon	Si	—	1.00
Chromium	Cr	16.0	18.0
Nickel	Ni	10.0	14.0
Molybdenum	Mo	2.00	3.00

Values per ASTM A194/A194M-24, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.

Physical properties (typical)

Density0.290 lb/in³ (8.03 g/cm³)

Modulus of elasticity28.0 × 10⁶ psi (193 GPa)

Thermal expansion (68–212 °F)8.9 µin/in·°F

MagneticNo in the annealed condition; slightly magnetic after cold work

Specifications & technical data

Mechanical properties.

Mechanical properties — ASTM A194 Grade 8M

Nut style and size (in.)	Proof load stress (ksi)	Hardness, min	Hardness, max
Heavy hex, all sizes	80	126 HBW / 60 HRB	300 HBW / 32 HRC
Hex (finished pattern), all sizes	75	126 HBW / 60 HRB	300 HBW / 32 HRC
Grade 8MA (solution treated in the finished condition), all sizes	80 heavy hex · 75 hex	126 HBW / 60 HRB	192 HBW / 90 HRB

Values per ASTM A194/A194M-24, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Jam nuts: 46 % of the tabulated proof load. Strain-hardened Grade 8 nuts (S1) are proof tested to 125 / 115 / 105 / 100 ksi heavy hex by size and hardness limits do not apply.

Heat treatmentGrade 8M nuts are hot or cold forged, or machined from hot-forged, hot-rolled or cold-drawn bar, with no heat-treatment requirement (A194 clause 6.6). The 8MA type is carbide solution treated after forging or machining (clause 6.7), which lowers hardness to the 126–192 HBW / 60–90 HRB window.

Standards

Specifications that apply.

ASTM A194 / ASME SA-194Nuts for bolts for high-pressure or high-temperature service

ASTM A193 / A320 Grade B8MCompanion studs

ASME B18.2.2Heavy hex nut dimensions

NACE MR0175 / ISO 15156316 is listed for sour service within its limits

Forms we supply

How A194 8M ships from Houston.

Heavy hex nuts (the default for pressure bolting)
Finished hex nuts
Jam nuts
Custom and special nuts to drawing

Companion grades

Companion studASTM A193 Grade B8M Class 1 (316 Stainless)

Economy alternativeASTM A194 Grade 8 (304 Stainless)

9 products in this grade

A194 8M fasteners we make.

All products →

Nuts A194 8M Finished Hex Nuts A194 8M Heavy Hex Nuts A194 8M Machine Screw Hex Nuts A194 8M Hex Jam Nuts A194 8M Lock Nuts A194 8M 12-Point Flange Nuts A194 8M Hexagon Cap Nuts A194 8M Tommy Bar Nuts A194 8M Casing Cap Nuts

Every item is manufactured to your drawing or standard in A194 8M, imperial or metric, with an EN 10204 3.1 certificate.

Where A194 8M is used

Offshore and marine flange boltingSeawater and desalination pipingChemical and pharmaceutical process equipmentCoastal plant and pulp-mill boltingSour service within NACE limits

The buyer’s guide

What is ASTM A194 Grade 8M?

Grade 8M is the 316 stainless member of the A194 Grade 8 family. Its 16 to 18 percent chromium, 10 to 14 percent nickel and 2 to 3 percent molybdenum give it a markedly better resistance to chloride pitting than 304, and the nut is otherwise identical to Grade 8: machined from solution-annealed bar, 80 ksi proof load, non-magnetic. Specify it with B8M studs so every part of the joint has the same corrosion resistance; mixing 304 nuts on 316 studs puts the weaker alloy in the crevice where pitting starts.

Preventing galling on stainless joints

Austenitic stainless threads weld to each other under pressure if they run dry. For 8M nuts we recommend one of three approaches: a molybdenum-disulfide or nickel-based anti-seize applied at assembly, a PTFE-coated stud with an oversize-tapped nut, or silver-plated nuts for high-temperature and vacuum service where organic lubricants are not permitted.

Testing, certification and marking

Hardness tested per lot; proof-load tested on request or where the specification requires it
Grade symbol 8M, or 8MB on nuts machined from bar (ASTM A194 Table 7), and manufacturer's identification on one face of every nut
EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
Oversize tapping for coated studs and PTFE / zinc / hot-dip galvanized finishes available

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