ISO 3506-3 Stainless Steel Set Screws
ISO 3506-3 specifies the mechanical and physical property requirements for stainless steel set screws and similar fasteners that are not subjected to tensile stress. The standard covers fasteners manufactured from corrosion-resistant austenitic and duplex stainless steels, with defined material grades and hardness classes. It establishes requirements for material composition, hardness, and proof torque for socket set screws, helping ensure consistent performance in applications where secure positioning and corrosion resistance are important.
Stainless steel set screws manufactured to ISO 3506-3 are available in various point styles and configurations to meet different fastening requirements. The standard covers metric threads from M1.6 to M24, with thread dimensions and tolerances based on the relevant ISO standards. These fasteners are commonly used to secure components such as gears, pulleys, shafts, and collars in machinery and industrial assemblies. Material grade and hardness class should be selected according to the required mechanical performance, corrosion resistance, and operating environment.
Dimension Standard:
Material Chemical Composition:
ISO 3506-3 specifies the chemical composition requirements for corrosion-resistant stainless steel set screws, covering austenitic and duplex stainless steel grades. The chemical composition determines important material characteristics, including corrosion resistance, strength, and suitability for different service environments. The following table summarizes the specified chemical composition limits for the applicable stainless steel grades, including the principal alloying elements and their permitted ranges.
| Stainless steel grade | Grade | C | Si | Mn | P | S | Cr | Ni | Mo | Cu | N | Other elements and notes |
| Austenitic | A1 | 0,12 | 1,00 | 6,5 | 0,020 | 0,15 to 0,35 | 16,0 to 19,0 | 5,0 to 10,0 | 0,70 | 1,75 to 2,25 | — | c,d,e |
| Austenitic | A2 | 0,10 | 1,00 | 2,00 | 0,050 | 0,030 | 15,0 to 20,0 | 8,0 to 19,0 | —ᶠ | 4,0 | — | g,h |
| Austenitic | A3 | 0,08 | 1,00 | 2,00 | 0,045 | 0,030 | 17,0 to 19,0 | 9,0 to 12,0 | —ᶠ | 1,00 | — | 5C ≤ Ti ≤ 0,80 and/or 10C ≤ Nb ≤ 1,00 |
| Austenitic | A4 | 0,08 | 1,00 | 2,00 | 0,045 | 0,030 | 16,0 to 18,5 | 10,0 to 15,0 | 2,00 to 3,00 | 4,0 | — | h,i |
| Austenitic | A5 | 0,08 | 1,00 | 2,00 | 0,045 | 0,030 | 16,0 to 18,5 | 10,5 to 14,0 | 2,00 to 3,00 | 1,00 | — | 5C ≤ Ti ≤ 0,80 and/or 10C ≤ Nb ≤ 1,00ⁱ |
| Austenitic | A8 | 0,030 | 1,00 | 2,00 | 0,040 | 0,030 | 19,0 to 22,0 | 17,5 to 26,0 | 6,0 to 7,0 | 1,50 | — | — |
| Duplex | D2 | 0,04 | 1,00 | 6,0 | 0,040 | 0,030 | 19,0 to 24,0 | 1,50 to 5,5 | 0,10 to 1,00 | 3,00 | 0,050 to 0,20 | Cr+3,3Mo+16N ≤ 24,0ʲ |
| Duplex | D4 | 0,04 | 1,00 | 6,0 | 0,040 | 0,030 | 21,0 to 25,0 | 1,00 to 5,5 | 0,10 to 2,00 | 3,00 | 0,050 to 0,30 | 24,0 < Cr+3,3Mo+16N ʲ |
| Duplex | D6 | 0,030 | 1,00 | 2,00 | 0,040 | 0,015 | 21,0 to 23,0 | 4,5 to 6,5 | 2,50 to 3,5 | — | 0,080 to 0,35 | — |
| Duplex | D8 | 0,030 | 1,00 | 2,00 | 0,035 | 0,015 | 24,0 to 26,0 | 6,0 to 8,0 | 3,00 to 4,5 | 2,50 | 0,20 to 0,35 | W ≤ 1,00 |
Hardness:
Hardness is an important mechanical property of stainless steel set screws, influencing their resistance to indentation and deformation under compressive loading. ISO 3506-3 defines hardness requirements for the specified stainless steel grades and hardness classes. The following table presents the applicable hardness classes and their corresponding requirements, providing a reference for material selection, quality inspection, and verification of product conformity.
| Test method | 12H min. | 12H max. | 21H min. | 21H max. |
| Vickers hardness, HV | 125.00 | 209.00 | 210.00 | — |
Proof Torque:
ISO 3506-3 specifies proof torque requirements for socket set screws to verify their ability to withstand a defined torsional load without unacceptable failure. The required proof torque depends on the applicable stainless steel grade, hardness class, and thread size. The following table summarizes the specified proof torque values for socket set screws covered by the standard. These requirements help assess torsional performance during installation and support quality control of finished fasteners.
| Nominal thread diameter d | Proof torque 12H (Nm) | Proof torque 21H (Nm) |
| 1,6 | 0,03 | 0,05 |
| 2.00 | 0,06 | 0,10 |
| 2,5 | 0,18 | 0,30 |
| 3.00 | 0,25 | 0,42 |
| 4.00 | 0,80 | 1,40 |
| 5.00 | 1,70 | 2,80 |
| 6.00 | 3,00 | 5,00 |
| 8.00 | 7,00 | 12,0 |
| 10.00 | 14,0 | 24,0 |
| 12.00 | 25,0 | 42,0 |
| 16.00 | 63,0 | 105.00 |
| 20.00 | 126.00 | 210.00 |
| 24.00 | 200.00 | 332.00 |