We’ve had more than a few calls with questions why the stainless self-drilling screws are magnetic. The customers reaction is that we sold them something that wasn’t stainless. That is a reasonable misconception. So, let’s clarify! The self-drilling screws and even some sheet metal screws are made out of 410 stainless. Here is a brief explanation…..
Grade 410 Bright Hardened Stainless Steel used in self-drilling (Tek) screws intended for steel substrates is a Martensitic alloy containing 12% chromium but no nickel. It is therefore somewhat less resistant to corrosive attack than the 300 Series grades. The reason for this is 300 series isn’t hard enough to keep a drill point. It is magnetic and is hardened by heat treatment which gives it the mechanical properties necessary to penetrate most metallic materials. It is recommended that these fasteners be used in thinner material. These fasteners are most popular for use in Aluminum.
It is also my understanding that the 410 stainless can be subject to a light surface rust (you see this a lot in marine cable ) but yet it is easily wiped off, and is not really considered a penetrating corroding rust.
Hope this helps!!!