Stainless steel fasteners are defined by the grade of the material. Now what exactly does this mean? See the list below for information on common grades of stainless steel fasteners including material and common applications.
Type 304: 17%-19% Chrome, 8%-12% Nickel, .08% Maximum Carbon. This is a superior grade of 18-8 stainless steel and is used for Machine Screws, Cap Screws, Sheet Metal Screws, Hex Cap Screws and all cold headed or hot forged fasteners. It is an equivalent to 18-8 Stainless Steel.
Type 305:17%-19% Chrome, 8%-10% Nickel, .12% Maximum Carbon. This grade has been developed specifically to improve the cold heading qualities of 18-8. This grade does not work-hardened products are actually made from this grade even though they are referred to as being made from type 304 Corrosion resistance and physical qualities are equal to Type 304.
Type 316:16%-18% Chrome, 10%-14% Nickel, .08% Maximum Carbon, 2.00% Maximum Molybdenum. This grade is greater corrosion resistance when used with certain acids as compared to general range of 18-8 stainless steel. 316 Stainless Steel is used in saltwater application such as boats and docks.
Type 18-8:18% Chrome, 8% Nickel, .08% Maximum Carbon. Used in most fasteners and is the standard.It is an equivalent to 304 Stainless Steel.
Type 410:11.5%-13.5% Chrome, .15% Maximum Carbon. This grade can be bright and hardened up to approximately 40 Rockwell C. This is used in roofing screws and finishing washers.
Stainless Steel Fasteners locking up? It’s probably thread galling, not the quality of the parts but the common problem of using stainless steel fasteners.
The beneficial nature of using stainless steel is that it is corrosion resistant. This property is due to the fact that stainless steel, among other alloys, generate a protective oxide surface film. Though this is beneficial as it provides corrosion and rust resistance, it can sometimes lead to problems with installation.
Thread Galling occurs during fastener tightening and installation. When pressure builds between the contacting surfaces of the male and female threads, the protective oxides or coatings begin to shear, causing high points, or imperfections in the raw material to become locked together. The increase in friction causes the two parts to seize or “lock-up”. In serious cases, this problem is even referred to as “cold welding”, which illustrates the severity of the issue. Often, galling can cause damage to the thread of the fastener, but it can still be removed. In severe cases, the two materials completely weld together preventing loosening of the parts, and adding the difficult step of a forced removal and new parts to the process. The frustrating aspect of this is that both the nut and bolt can clear inspection individually, but fail to function effectively as a mechanical unit.
Though this problem may be frustrating, it is avoidable. The main issue to address is to decrease the friction between the adjoining parts. This can be done in several ways including a slower installation process (RPMs). The idea behind this method is to reduce the friction (and thus heat), between the parts preventing the “welding” process. Our recommended method, due to its ease of implementation, is lubrication. Common methods include specially designed lubricants and waxes, however due to its safety and ease of availability, we recommend dipping the bolt in Maalox.
Update: Maalox is no longer sold at stores so we started carrying an anti-seize solution that we’ve tested ourselves.
MRO Anti Seize solutions are tested lubricants with carefully manufactured specifications. Each type has unique characteristics which can be found on the individual product pages. We carry several different kinds of anti-seize to make sure we can offer a solution that works for you!
Anti-seize solutions offer many benefits to fastener installations. Not only do they provide fasteners with a layer of lubrication that reduces friction, the coating also creates an extra layer of lubrication and corrosion resistance to make your fastener assembly last even longer!
Other precautionary measures include using coarse threaded fasteners, using different grades of stainless steel for adjoining parts (take the corrosion resistance differences into consideration), and understanding the proper use of lock nuts. Because they are designed to add resistance to the existing threads of the bolt, it is best practice to make sure that a minimal amount of threads extend beyond the nut.
Reducing friction is the preemptive strike against this problem. That is why we recommend lubrication, and MRO anti-seize specifically, due to many of its properties beneficial to both sore stomachs and stainless steel. Galling can be a frustrating problem, but it can be prevented.
Stainless Steel Grades, Applications and Magnetism
Today, we will look at different grades of stainless steel 18/8, 304, A2, 316, A4 and 410 that are magnetic and non magnetic, or so they say. I am emailed all of the time “Why is this bolt magnetic?” Most common grades of stainless steel are magnetic in some degree. In fact, all of the stainless steel coming into the USA from china and other countries are magnetic in some form. 18/8, 304, A2 and 410 are more magnetic than 316 or A4 stainless steel. The most common grade of stainless steel is 304, or as referred to 18/8, and in metric A2. The second most common grade is 316 which is used in salt water application marine grade, food prep equipment, surgical, medical and pharmaceutical applications. 316 Stainless steel is used in these areas to minimize metallic contamination. 316 stainless is used in marine applications due to its increased resistance to chloride corrosion compared to 304, 18/8, A2 or 410 stainless steel. Also most high-end watches are made with 316 stainless. 410 Stainless steel is used in most construction fasteners when a high strength iron chromium water-resistant product is required, but less corrosion resistant to water.
18/8, 304 and A2 are used in most common construction projects, telecom, car, truck and trailer restoration, playgrounds that are exposed to the elements of natural rain water. These grades are all magnetic. Here is a sample of 304 18/8 Stainless Steel
316 And A4 are used in food prep manufacturing equipment, salt water marine application, surgical and pharmaceutical equipment and products. Watches are made from 316 or A4 stainless steel. Partially magnetic. Here is a sample of 316 Stainless Steel
410 Is used in most construction fasteners in exterior application exposed to the elements. These fasteners are used in standard rain water application where there is no salt water exposure. 410 are magnetic. Here is a sample of 410 Stainless Steel