Still researching this issue, but found this which although pretty technical does describe stainless fixings very comprehensively.
There are several misconceptions about stainless steel bolts and other fasteners. This guide is intended to clear up some common misunderstandings, but in a format that that is short and simplified.
1. Stainless Steel is Stainless Steel.
Not at all true. Steel is an alloy of Iron and trace amounts of Carbon, with some other elements in the mix, too. Making stainless steel requires the addition of other alloying agents, among them are chromium, manganese, molybdenum, nickel, phosphorous, silicon, and/or sulfur. Depending on the amount of these and other elements, many different grades of stainless steel can be produced and there are several grades suitable for making bolts and other fasteners with. The most common stainless steel is some version of "18-8"--that is, using approximately 18% chromium and 8% nickel. Common grades of stainless steel are 410 (Also called C1), 302, 304 (302 and 304 are also called A2), 305, and 316 (Also called A4). ( a version of 316 with additional molybdenum is labeled "2343") I've listed those grades in bold ordered from lowest corrosion resistance to highest corrosion resistance. Of the boltmakng alloys listed above, 302, 304, 305 are all based on "18-8" stainless. Put another way: If you ask the seller what kind of stainless steel his products are made from, and he says "18-8" or "A2", he hasn't told you much because there are various versions of 18-8, and at least two versions of "A2" stainless steel. F593C is an American Society for Testing and Materials (ASTM) specification for 304 stainless steel.
2. Stainless steel bolts are stronger than ordinary steel bolts
This is clearly not true for the majority of stainless steel bolts. Stainless steel in general has very little carbon, and because of that, most grades of stainless steel cannot be hardened by heat treatment. Stainless steel bolts are, in most cases, just slightly stronger than Grade 2 hardware store junk bolts, and in nearly all cases, significantly less than Grade 5. You do NOT want to use common-grade stainless fasteners in any application that would call for a hardened (Grade 5 or Grade 8, or stronger) fastener. ARP makes a fine line of stainless bolts that have a tensile strength of approximately 170,000 lbs per square inch. This is greater tensile strength than a typical Grade 8 fastener, but keep in mind that tensile strength is not the only measure of bolt quality/strength. Common grades of stainless steel may have reasonable tensile strength, but significantly less yield strength than a "regular" steel bolt--the stainless bolts are more "stretchy". Those ARP-made bolts are the ONLY stainless fasteners I'm aware of that are suitable for general use. There may be others--if you know of any, please let me know!
3. Stainless steel doesn't corrode
Stainless steel is more correctly called "corrosion resistant" steel. Some grades are more resistant to corrosion than others, and grades have been developed that are highly resistant to corrosion caused by specific uses: for example, 304 is subject to pitting when used in an environment heavy in chlorides, while 316 is less reactive to chloride.
4. Stainless Steel is not magnetic
Stainless in general tends to be LESS magnetic than "ordinary" steel, and some grades are non-magnetic. Stainless steel bolts can become slightly magnetic when processed by cold working. Even though the "raw material" going into the boltmaking machines is non-magnetic, the process of forming the head and threads may cause the bolts coming out of the machine to be somewhat magnetic.
5. Rolled threads are somehow "special".
It is absolutely true that rolled threads are better than cut threads in terms of strength and accuracy. But since NOBODY produces common-sized bolts by cutting the threads, it's kind of pointless to brag about rolled threads! In a production environment, it's actually cheaper to roll the threads rather than cut them, and it produces better results because the threads are "forged" and the grain of the metal is pressed into shape, while with cut threads the grain of the metal is disturbed by the cutting process. Huge diameter fasteners of low production volume, or "ready rod", long lengths of threaded rod, may--or may not--have cut threads. Still, ordinary-sized bolts will have rolled threads.
I received a communication of interest from eBay member alleygnat. In it, he told me:
"I would add one additional item to your discussion regarding rolled threads: Though it it correct that rolled threads are stronger due to the residual work left in them, residual stress can be relieved at prolonged exposure to elevated temperatures thus eliminating any benefit. However, more important to the topic is that threads with residual work (Rolled Threads) are far less corrosion resistant than cut threads. I've seen many a boat with rust running down the hull from bolts with oxidized threads with still bright heads."
I have not verified his claim that rolled threads are susceptible to corrosion more than cut threads.
Another issue with common grades of stainless steel is that the threads often seize ("gall") between the bolt and the nut. I suggest the use of an anti-seize compound, coupled to CAREFUL USE OF THE TORQUE WRENCH when tightening stainless steel. You MUST use a torque setting on the wrench suitable for the mechanical limits of the fastener, as adjusted for the reduced thread friction inherent when using a thread lubricant like anti-sieze compounds. As a rule of thumb, and unless the manufacturer says otherwise: Consider a stainless steel fastener to be capable of Grade 2 torque loads, and then adjust the torque DOWNWARD by 20% because of the lubricant properties of the anti-sieze.
Example: A common 304 (A2) 3/8-16 stainless bolt should accept the same torque as a 3/8-16 Grade 2 bolt--only about 20 ft/lbs. But since you've lubricated the threads with anti-seize compound, you'd reduce the torque by 20%, for a torque-wrench-setting of 16 ft/lbs. That is NOT VERY MUCH for a 3/8 bolt!!! There are stronger stainless bolts--some but not all 316 alloy bolts will take almost but not quite Grade 5 torque specs, but again you must adjust downward when you use anti-sieze. If you're used to working with hardened fasteners (Grade 5 and Grade
you won't believe how little torque is the maximum acceptable amount.
Generally, a manufacturer will put a trade mark of some sort on the bolt head. For example, many stainless steel bolts have the initials "THE" in raised letters on the bolt head. The THE signifies the bolt was made by Tong Hwei Enterprises, somewhere in the Far East--most likely Taiwan, although THE has factories in China and Malaysia as well.
