HOLO-KROME 72132 5/16-18 X 1-1/2吋 內六角螺絲 | 六角驅動 | 合金鋼 熱處理黑色氧化 (100 / 包)

I used a handful of these to rebuild a jig fixture, and the black oxide finish held up well against minor coolant splashes. The hex socket drive engaged cleanly without any stripping, which was my main worry.

Swapping out old hardware on my milling machine, these bolts went in smooth and the black oxide finish seems like it'll resist rust much better than the plain steel ones I had before. The hex drive seated perfectly with no stripping.

I used these to fasten some jig plates on my milling machine and the hex drive seated perfectly without any cam-out. The alloy steel feels sturdy enough for heavy clamping, and all 100 screws came with clean threads.