The Scoop On Stainless.

A question we are often asked at Uneeda Bolt is: “What are the differences between the types of stainless steel?” or “Why would someone use stainless steel over steel parts, and what kind should I use?”

Let’s start with steel. There are multiple classes of steel: from Carbon Steel and Alloy Steel, to Tool Steel.

These steels have very low resistance to corrosion in most instances. Some coatings that are applied over the raw material can aid the fastener in surviving harsh conditions for a little while, but ultimately, they are rated for a limited number of hours in a salt spray lab.

When customers ask for corrosive resistance properties beyond what steel can provide, we often inform them about stainless steel. Like steel, there are many different alloys/grades of stainless steel. Each one varies by hardness and corrosive resistance properties.

400 Series S/S – 400 series can be heat treated. Heat-treated 400 series has great hardness properties, but much less corrosion resistance than other types of stainless steel listed below.

Self-tapping, self-drilling, and other fasteners that require hardness are often made from this grade of stainless steel because it provides the strength required in most applications, while still providing better anti-corrosion properties than steel. Many people choose to zinc plate their 410 stainless as well: zinc plating acts as a lubricant when installing, creates a barrier between the raw material and the application material, as well as being sacrificial in order to improve weathering properties. 400 series is magnetic; this is important because many original equipment manufacturers rely on magnetic bit holders in assembly.

302-304 S/S (18/8) – Often referred to as 18/8 stainless, this material is a general term for any grade stainless between 302 and 304. It gets its name for being an alloy containing 18% chromium and 8% nickel. This stainless steel is much more corrosion resistant than the 400 series previously mentioned. While this grade of stainless steel will not “rot,” it can bleed rusty color due to impurities being brought to the surface during the manufacturing process. This why 18/8 stainless should always be passivated.

Passivating removes the impurities and reduces the chance that color will bleed from the hardware (every 18/8 screw that Uneeda provides has been passivated). This type of hardware is often used in wet, outdoor environments. Because it is softer than 400 series stainless, it can only be used in certain applications where shear, tensile, drill, and cut strength of the fastener is a non-issue.

302 HQ (XM7) – Similar to 18/8 in corrosion resistance, this stainless steel is 300 series with 3% copper added in order to improve the material’s cold-working/forming ability. Because less work hardening occurs during the manufacturing process, these parts are softer because they are less subject to work hardening, yet tougher (even in insanely cold temperatures) than its 18/8 cousin. Deck screws are often made from 302HQ because it is less likely to snap during installation.

316 S/S – Also known as “surgical grade stainless steel,” this material is used often in environments next to bodies of saltwater, body jewelry, restaurant counters, and surgical tools. The reason this stainless steel is used in harsh environments where salt, chlorine, and other aggressive chemicals are used is that 316 stainless steel does not bleed its color and will never show any signs of rust under any circumstances. Can you imagine if a surgeon was operating with rusty scalpels and forceps? Like 18/8, this grade of stainless is extremely soft. This is the most expensive option when it comes to stainless steel fasteners.

If you have more questions pertaining to stainless steel, contact us! We will answer to the best of our ability.

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