Internal teeth dig into the screw head while the smooth outside edge won't snag objects. These washers provide greater vibration resistance than split lock washers. Use with fasteners that have small heads, such as fillister and cheese head screws. Manufactured from 410 Series Martensitic Stainless Steel. 410 is a stainless alloy that has a higher hardness than 18-8 Stainless Steel but is less corrosion resistant than 18-8 and will be magnetic.