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Stainless Steel 321/321H Screws are titanium-stabilized austenitic fasteners designed for high-temperature and corrosive operating environments where conventional stainless steels begin to lose structural integrity. Manufactured under standards such as ASTM A193, ASTM A276, DIN 933, and ISO 3506, these screws are widely used in aerospace assemblies, petrochemical processing units, thermal power plants, and exhaust systems where oxidation resistance and creep strength are critical.
Unlike standard SS 304 or SS 316 fasteners, SS 321/321H screws offer enhanced resistance to intergranular corrosion due to titanium stabilization, making them suitable for continuous service in elevated temperature conditions up to approximately 900°C (depending on load conditions). The “H” variant provides higher carbon content for improved strength retention at elevated temperatures.
KK Fasteners supplies Stainless Steel 321/321H Screws to global engineering industries with strict adherence to dimensional accuracy, material traceability, and international export standards, ensuring consistent performance across critical applications.
| Parameter | Specification |
|---|---|
| Material Grades | SS 321, SS 321H (Titanium Stabilized Austenitic Stainless Steel) |
| Standards | ASTM A193, ASTM A276, DIN 933, DIN 931, ISO 3506 |
| Size Range | M2 to M36 / #2 to 1-1/2 inch |
| Thread Types | Metric Coarse, Metric Fine, UNC, UNF |
| Strength Grade | A2-70 equivalent, High-temperature Grade 321H |
| Finish | Bright, Passivated, Polished, Black Oxide (on request) |
| Head Types | Hex Head, Socket Head, Pan Head, Countersunk |
| Hardness | Up to 95 HRB (depending on heat treatment) |
| Tensile Strength | Up to 515–750 MPa (grade dependent) |
Grade |
C |
Mn |
Si |
P |
S |
Cr |
Mo |
Ni |
N |
|
321/321H |
min.
max. |
-
0.080 |
-
2 |
-
1 |
-
0.045 |
-
0.030 |
-
19 |
-
- |
-
13 |
-
- |
Grade |
Tensile Strength (MPa) min |
Yield Strength 0.2% Proof (MPa) min |
Elongation (% in 50mm) min |
Hardness |
|
Rockwell B (HR B) max |
Brinell (HB) max |
||||
321/321H |
515 MPa |
205 MPa |
40% |
95 |
217 |
Grade |
Density (kg/m3) |
Elastic Modulus (GPa) |
Mean Coefficient of Thermal Expansion (μm/m/°C) |
Thermal Conductivity (W/m.K) |
Specific Heat 0-100 °C (J/kg.K) |
Electrical Resistivity (nΩ.m) |
|||
|---|---|---|---|---|---|---|---|---|---|
0-100 °C |
0-315 °C |
0-538 °C |
at 100 °C |
at 500 °C |
|||||
321/321H |
8027 |
193 |
16.6 |
17.2 |
18.6 |
16.1 |
22.2 |
500 |
720 |
Flat Head Machine Screws
| Nominal Size | A | H | J | T | M | G | N | Phillips Driver Size | |||||
| Head Diameter | Height of Head | Width of Slot | Depth of Slot | Dimensions of Recess | |||||||||
| Diameter | Depth | Width | |||||||||||
| Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | ||
| 2 4 5 6 7* 8 9* 10 12 14* 1/4 5/16 3/8 1/2 | .172 .225 .252 .279 .305 .332 .358 .385 .438 .491 .507 .635 .762 .875 | 147 .195 .220 .244 .268 .292 .316 .340 .389 .437 .452 .568 .685 775 | .051 .067 .075 .083 .091 .100 .108 .116 .132 .148 .153 .191 .230 .223 | .040 .055 .062 .069 .076 .084 .091 .098 .112 .127 .131 .165 .200 .198 | .031 .039 .043 .048 .048 .054 .054 .060 .067 .075 .075 .084 .094 .106 | .023 .031 .035 .039 .039 .045 .045 .050 .056 .064 .064 .072 .081 .091 | .023 .030 .034 .038 .041 .045 .049 .053 .060 .068 .070 .088 .106 .103 | .015 .020 .022 .024 .027 .029 .032 .034 .039 .044 .046 .058 .070 .065 | .102 .128 .154 .174 .182 .189 .258 .204 .268 .283 .283 .365 .393 .424 | .089 .115 .141 .161 .169 .176 .245 .191 .255 .270 .270 .352 .380 .411 | .063 .089 .086 .106 .114 .121 .146 .136 .156 .171 .171 .216 .245 .276 | .017 .018 .027 .029 .030 .031 .034 .032 .036 .039 .035 .061 .065 .069 | 1 1 2 2 2 2 2 2-3* 3 3 3 4 4 4 |
| Nominal Size | A | W | H | F | U | J | T | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Width Across Flats | Width Across Corners | Height of Head | Diameter of Washer | Thickness of Washer | Width of Slot | Depth of Slot | |||||||
| Max. | Min. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | |
| 4 6 7 8 10 12 14 1/4 5/16 3/8 | .187 .250 .250 .250 .312 .312 .438 .375 .500 .562 | .181 .244 .244 .244 .305 .305 .428 .367 .489 .551 | .202 .272 .272 .272 .340 .340 .409 .409 .545 .614 | .060 .093 .093 .110 .120 .155 .190 .190 .230 .295 | .049 .080 .080 .096 .105 .139 .172 .172 .208 .270 | .243 .328 .328 .348 .414 .432 .520 .520 .676 .780 | .225 .302 .302 .322 .384 .398 .480 .480 .624 .720 | .019 .025 .029 .031 .031 .039 .050 .050 .055 .063 | .011 .015 .017 .019 .019 .022 .030 .030 .035 .037 | .039 .048 .048 .054 .060 .067 .075 .075 .084 .094 | .031 .039 .039 .045 .050 .056 .064 .064 .072 .081 | .042 .053 .062 .074 .080 .103 .111 .111 .134 .168 | .025 .033 .040 .052 .057 .077 .083 .083 100 .131 |
|
Nominal
|
Thread.
|
Hex Socket Size
|
Body diameter and Head height
|
Head Dia
|
Soc. length
|
||
|
Size
|
Pitch
|
Max
|
Min
|
Max
|
Min
|
||
|
J
|
D /H
|
A
|
K
|
||||
|
M3
|
0.5
|
2.50
|
3.00
|
2.86
|
5.50
|
5.20
|
1.3
|
|
M4
|
0.70
|
3.00
|
4.00
|
3.82
|
7.00
|
6.64
|
2.00
|
|
M5
|
0.8
|
4.00
|
5.00
|
4.82
|
8.50
|
8.14
|
2.70
|
|
M6
|
1.0
|
5.00
|
6.00
|
5.82
|
10.00
|
9.64
|
3.30
|
|
M8
|
1.25
|
6.00
|
8.00
|
7.78
|
13.00
|
12.57
|
4.3
|
|
M10
|
1.5
|
8.00
|
10.00
|
9.78
|
16.00
|
15.57
|
5.50
|
|
M12
|
1.75
|
10.00
|
12.00
|
11.73
|
18.00
|
17.57
|
6.60
|
|
M16
|
2.0
|
14.00
|
16.00
|
15.73
|
24.00
|
23.48
|
8.80
|
|
M20
|
2.5
|
17.00
|
20.00
|
19.67
|
30.00
|
29.48
|
10.70
|
|
M24
|
3.0
|
19.00
|
24.00
|
23.67
|
36.00
|
35.38
|
12.90
|
Stainless Steel 321/321H Screws are used wherever components are exposed to sustained heat, mechanical stress, and corrosive environments requiring long-term stability.
Stainless Steel 321/321H Screws are manufactured using controlled cold forging and precision CNC thread rolling processes to ensure dimensional consistency and mechanical strength. Heat treatment cycles are carefully monitored to maintain alloy stability without compromising corrosion resistance.
Each batch undergoes stringent quality inspections including dimensional verification, hardness testing, tensile strength validation, and surface passivation checks. Full material traceability is maintained through heat number tracking and certification records. KK Fasteners integrates ISO 9001:2015-compliant quality systems to ensure every fastener meets international industrial requirements before dispatch.
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Stainless Steel 321/321H Screws are titanium-stabilized austenitic fasteners designed for high-temperature environments. They resist intergranular corrosion and oxidation, making them suitable for aerospace, petrochemical, and thermal processing equipment where sustained heat exposure affects standard stainless steels.
SS 321 contains titanium stabilization for improved corrosion resistance, while SS 321H has a higher carbon content, which increases tensile strength and creep resistance. SS 321H is preferred for long-term structural applications exposed to elevated temperatures and continuous mechanical stress.
These screws are commonly manufactured under ASTM A193, ASTM A276, DIN 933, DIN 931, and ISO 3506 standards. These specifications ensure consistent mechanical performance, dimensional accuracy, and compatibility with global industrial requirements.
They are widely used in aerospace engine assemblies, petrochemical processing units, power generation plants, automotive exhaust systems, and industrial furnaces. These applications require fasteners that maintain strength and stability under high-temperature conditions.
A reliable supplier should provide ISO-certified production, full material traceability, compliance with international standards, and consistent quality testing. KK Fasteners supports global buyers with certified manufacturing, inspection reports, and export-ready documentation for industrial applications.
Stainless Steel 321/321H Screws deliver dependable performance in high-heat, high-stress environments where standard fasteners fail prematurely. With precision manufacturing and certified material traceability, KK Fasteners supports global industries with engineered fastening solutions tailored to critical applications.
Request technical drawings or a customized quotation to align specifications with your project requirements and procurement standards.
