内六角螺钉（Allen Key螺栓）完整指南：应用与选型

Both are high-strength alloy steel. Grade 12.9 has minimum tensile strength of 1200 MPa vs 1040 MPa for Grade 10.9, and yield strength of 1100 MPa vs 940 MPa. Grade 12.9 also has a dark gray phosphate coating as standard while 10.9 is typically zinc-plated. For critical high-stress machinery connections (engines, gearboxes, cranes), use Grade 12.9. For general industrial equipment, Grade 10.9 is adequate and more cost-effective.

Yes, socket head cap screws can be used with nuts as an alternative to hex bolts. However, since the screw head is designed to bear directly on the joint material (not a nut), using a socket head cap screw with a nut is less efficient than using a proper hex bolt or machine screw with a nut. Socket head cap screws are designed for female thread engagement in a tapped hole.

The most common causes of socket stripping are: incorrect allen key size causing cam-out and rounding; over-torquing beyond the screw's yield strength; cross-threading during initial engagement; corrosion or debris in the threads. Always use the correct size tool, apply lubricant, start threading by hand to verify alignment, and use a torque wrench for critical applications.