8-18 x 2 Slotted Indented Hex Washer Self Drilling Screw Full Thread Zinc & Bake 8-32 064-105 and the square head helps

and the square head helps to prevent the bolt from turning when it is tightened

The M12 x 60 DIN 931 10

this washer effectively distributes load

and it is also self-locking

These 2-56 x 1/8 Phillips Fillister Head Machine Screws are fully threaded and made of zinc-plated steel

8-18 x 2 Slotted Indented Hex Washer Self Drilling Screw Full Thread Zinc & Bake 8-32 064-105 and the square head helpsThese 8 18 x 2 Slotted Indented Hex Washer Self Drilling Screw Full Thread Zinc & Bake are designed for fastening metal to metal. They have a slotted indented hex washer head that provides a large bearing surface and helps to prevent the screw from stripping. The self drilling point eliminates the need for pre drilling, saving time and effort. The full thread design provides maximum holding power. These screws are zinc plated for corrosion resistance