stainless steel bolts FAQ

There are a lot of stainless steels. Some are more magnetic than others, corrosion resistance varies widely. Short answer = no general answer:

Can't tell from looking, but they look very shiny, like a plating. I'd see what a magnet does, though some alloys are somewhat magnetic.

As others point out some grades of stainless are magnetic.

Looking it up I see there are tests you can run:

https://www.waterbottle.tech/simple-methods-for-identifying-stainless-steel/ Been a long time but I remember running tests on various grades to see if they would stand up to making polymers under highly acidic conditions. You might do something similar to see if they will hold up under the use you are putting them to.

If the pic is of the actual bolts... The bolts do not look like stainless - they look like low quality steel bolts plated with zinc. The manufacturing looks poor. IMO, they are the 13 cent variety, not the $1.13 variety. Same for the nuts. They are the 5 cent variety, not the 55 cent variety. There is low quality stainless but I have never seen that used in nuts and bolts. Threaded pieces are normally 18-8 or better and have better machining.

cheap-assed chinese electro-zinc plated grade 2 would be my guess. What markings *(if any) on the head?

Whar are the tip-offs in the picture that they ared ow quality?

It's difficult to say for sure with out viewing the head markings or seeing better photos. It could be the small pixel count of the photo or the zinc plating, but... the machining just does not look crisp / sharp. There are striations on the bolt head and nut that are not seen on quality bolts and nuts. The nut appears to be much thinner than a good quality nut.

There are good fasteners, crappy fasteners, and the very worst, electrician-grade fasteners.

Striations are a bad sign and so are threads that aren't cut sharply, or even worse appear to be rolled rather than cut.

--scott

You're right, it's difficult to say with certainty. There are chemical and spark tests which I linked in a reply the other day which are much better than images.

Here are M5 ULS stainless we sell in a parts packet:

Typical SNP steel ULS:

depending on the camera and lighting they look pretty much similar.

The saw tooth matks on the flats and the fact there is no chamfer at the end of the thread and the fact I've seen WAY TOO MANY of those absolutely TERRIBLE fasteners. Also the absolutely S***TY cut (not rolled) threads that look like they would sieze up and strip the first time you put any torque on them.

ALL Quality bolts have roll-formed threads. Cut or in this case "torn" or "chewed" threads are almost exclusively the domain of cheap crappy fasteners. These are definitely NOT rolled threads and appear to have been cut with a worn out harbor fright dieset - - -

Having had experience with high quality bolts would be a start. Then look at the thread - that is visibly of poor quality, as is the shaping of the head of the bolt. Overall, looks like cheap Chinese s*it!

Rolled threads can have some advantages over cut threads. It depends on the material and the application. They are not always inferior.

I never thought of looking at the head of the bolt, which does have soem "secret code" written on it as you can see in the photo of the head here.

Thanks for looking at the threads. Here's a clearer picture of them.

Grade 4.8 is a standard for fasteners like bolts, screws, and studs, which are made from low or medium carbon alloy steel. The numbers on fasteners, such as 4.8, 8.8, 10.9, or 12.9, indicate the tensile strength in the first digit and the yield strength in the second digit.

Here are some characteristics of Grade 4.8 fasteners: Tensile strength: For low carbon steel, the tensile strength is around

Core hardness: The core hardness is between B71–95 on the Rockwell scale.

Size range: The size range for a fully or partially annealed Grade 4.8 screw is between M5 to M100.

Uses: Grade 4.8 fasteners are used in mechanical equipment, buildings, bridges, tunnels, and high speed railways.

Strength: Grade 4.8 bolts are commonly referred to as high strength bolts.

Metric low grade carbon steel bolt:

In some other contexts, I've seen it stand for Quanjiangcun, a manufacturing district in China. Not sure if that applies here. Probably not.