Precautions for Grade 12.9 DIN912 Hexagon Socket Head Cap Screws

1. Recommended Tightening Torque**: The recommended tightening torque for Grade 12.9 DIN912 screws is 60%~70% of the proof load, to avoid yielding or fracture caused by over torque. Exact values shall be calculated precisely according to thread size and friction coefficient. Over torque tightening is strictly prohibited.

2. Applicable Temperature Range**: Standard Grade 12.9 screws are suitable for temperatures from ** 50℃ to +150℃**. High temperature resistant alloy steel shall be adopted for temperatures above 150℃, and mechanical properties shall be re verified for temperatures above 250℃.

3. Hydrogen Embrittlement Prevention**: Grade 12.9 screws after electro galvanizing must undergo hydrogen embrittlement relief treatment followed by hydrogen embrittlement inspection. Non conforming products are strictly forbidden for use. For long term stored galvanized Grade 12.9 screws, hydrogen embrittlement risk shall be re inspected before application.

4. Tool Matching**: Standard hex socket wrenches of corresponding sizes must be used. Worn or deformed tools are strictly prohibited to prevent slipping and damage of the hex socket hole, which may cause non removability or head fracture.

5. Application in Vibration Environments**: Anti loosening measures (e.g., lock nuts, thread locker adhesives, disc springs) must be applied under vibration and impact conditions to prevent loosening. The anti loosening solution of plain washers plus spring washers alone is not recommended.

6. Prohibited Application Scenarios**: Strictly prohibited for scenarios under transverse shear load (the socket head structure has weak shear resistance); prohibited for highly corrosive environments (anti corrosion coatings or stainless steel materials are required); prohibited for scenarios with repeated impact loads exceeding the fatigue limit.

7. Installation Notes**: Clean iron filings and oil contaminants in threaded holes before installation to avoid abnormal torque caused by thread jamming. Ensure the screw is perpendicular to the connected component during tightening to prevent head fracture due to eccentric load.