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Stainless Steel 304H Screws are high-carbon austenitic fasteners engineered for elevated temperature service where standard 304 grade may lose mechanical stability. With improved carbon content (0.04–0.10%), these screws deliver enhanced creep resistance and superior strength retention in continuous high-heat environments such as boilers, heat exchangers, refinery piping systems, and power generation equipment. They are widely specified under ASTM and ASME standards for structural integrity under thermal stress.
These screws are commonly used in industries requiring long-term exposure to temperatures above 500°C, where oxidation resistance and mechanical reliability are critical. KK Fasteners supplies precision-engineered SS 304H fasteners to global OEMs and EPC contractors, ensuring full material traceability and compliance with international standards for critical applications.
| Parameter | Specification |
|---|---|
| Material Variants | Stainless Steel 304H (AISI 304H), 304, 316, 316L |
| Grade Options | 304H (High Carbon Austenitic Grade) |
| Size Range | M3 to M64 / #6 to 2.5 inch |
| Thread Type | Metric (ISO), UNC, UNF, BSF |
| Applicable Standards | ASTM A193, ASTM A194, ISO 3506, DIN 933, DIN 931 |
| Surface Finish | Bright, Passivated, Polished, Black Oxide |
| Type Variants | Hex Head, Socket Head, Machine Screws, Stud Bolts |
| Tensile Strength | ≥ 515 MPa (typical for 304H condition) |
| Hardness | Up to 201 HB max (annealed condition) |
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N | |
| 304H | min. | – | – | – | – | – | 18.0 | – | 8.0 | – |
| max. | 0.08 | 2.0 | 0.75 | 0.045 | 0.030 | 20.0 | 10.5 | 0.10 | ||
| 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 | ||||
| 304H | 515 | 205 | 40 | 92 | 201 |
| Grade | Density (kg/m3) | Elastic Modulus (GPa) | Mean Coefficient of Thermal Expansion (m/m/0C) | Thermal Conductivity (W/m.K) | Specific Heat 0-1000C (J/kg.K) | Electrical Resistivity (n.m) | |||
| 0-1000C | 0-3150C | 0-5380C | at 1000C | at 5000C | |||||
| 304H | 8000 | 193 | 17.2 | 17.8 | 18.4 | 16.2 | 21.5 | 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 304H Screws are primarily used in high-temperature and pressure-intensive environments where standard fasteners cannot maintain long-term stability.
The production of Stainless Steel 304H Screws involves precision cold forging followed by CNC thread rolling to ensure uniform grain flow and mechanical strength. Heat treatment is carefully controlled to stabilize the austenitic structure without compromising carbon distribution.
Each batch undergoes strict dimensional inspection, tensile testing, and hardness verification to ensure compliance with ASTM A193 and ISO 3506 standards. Surface finishing is validated for corrosion resistance and uniformity, especially for passivated variants.
KK Fasteners implements full lot traceability across production cycles, ensuring every fastener can be traced back to its raw material heat number. This ensures reliability in critical industrial applications where failure is not an option.
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Stainless Steel 304H Screws are high-carbon austenitic fasteners designed for high-temperature service. They offer improved creep strength and better mechanical stability compared to standard 304 screws, making them suitable for boilers, heat exchangers, and refinery equipment exposed to continuous heat.
Yes. 304H contains a higher carbon content, which improves its ability to retain strength at elevated temperatures above 500°C. While 304 is used for general applications, 304H is preferred for long-term thermal exposure in power plants, furnaces, and process industries.
SS 304H screws are commonly manufactured according to ASTM A193, ASTM A194, ISO 3506, DIN 933, and DIN 931 standards. These ensure proper mechanical properties, dimensional accuracy, and suitability for pressure and temperature-critical applications.
Selection depends on operating temperature, load conditions, and environmental exposure. 304H is ideal for high-heat environments above 500°C. Thread type, head style, and coating should be selected based on torque requirements and assembly design.
Choose a supplier with ISO certification, ASTM compliance, material traceability, and proven export experience. Reliable manufacturers provide test certificates, inspection reports, and consistent global supply capability.
Stainless Steel 304H Screws are critical for high-temperature reliability in demanding industrial systems where failure is not an option. With precision manufacturing, strict ASTM compliance, and global supply capability, KK Fasteners supports OEMs and EPC contractors with dependable fastening solutions. Contact the engineering team for technical drawings, pricing, or custom specification support tailored to your project requirements
