M16-2 x 40mm 內六角螺絲 | 平頭內六角驅動 | 全螺紋 | 12.9級合金鋼 熱處理黑色氧化 (50 / 包)

The black oxide finish looks even better in person and held up perfectly when I torqued them into my tooling fixture. The hex socket drive seated cleanly with no stripping, and the 12.9 grade gives me confidence they won't fatigue under load.

I needed these for a jig I was building, and the thermal black oxide coating seems tough—no scratches after driving several in. The hex socket drove true without any cam-out, which I appreciated. Solid little fasteners.

The flat head sits flush perfectly on my jig fixture, and the black oxide finish resisted oil staining during a long machining run. These are exactly the strength I needed for heavy clamping loads.