M6-1 X 20mm 內六角圓柱頭螺絲 | 平頭內六角驅動 | 全牙 | 12.9級合金鋼鍍鋅（2500/包）

The hex socket drive grabs perfectly with my Allen key, no stripping even on the 20mm length. I’ve used a handful for jig fixtures and they hold tight under vibration, and the zinc plating hasn’t shown a speck of rust yet.

Just a perfect fit for the jig I'm building—the flat heads seat flush without any wobble, and the zinc plating looks clean.

The zinc plating on these M6-1 screws seems consistent across the 2500 pieces, which is what I needed for a large tooling run. I do wish the flat head was slightly more countersunk, but the hex socket drive bit into all my jigs cleanly. They've held up fine so far.