M4-0.7 X 55mm 內六角螺絲 | 六角驅動 | 部分螺紋 | 12.9級合金鋼熱處理黑色氧化 (300顆/包)

Installed these in a robotics fixture and the hex socket drive handled high torque without stripping. The thermal black oxide finish looks clean and seems to resist minor corrosion well.

Needed exactly 300 for a custom jig build, and every single screw threaded in smoothly without any binding. The 12.9 alloy steel feels reassuringly solid, and the black oxide finish looks clean and professional.

The black oxide finish on these screws gives them a nice uniform look, and the hex socket drive grips the wrench firmly without any wobble. I’ve used a few dozen already in a jig build and not a single one has stripped or snapped.