What does “stainless steel back” mean on a watch?

Search the phrase and you get shop listings, a forum thread and a few blogs. Some say it means the watch is stainless steel, and others say it means the watch is cheap. None cites the rule the words come from. Below: what the words cover, where they come from, nine customs rulings that say what the rest of such a case was made of, and how to read your own case back.

First, the words on the back

A watch case is the metal housing that holds the movement, the works that keep time, and the old US rules listed its parts as "the back, center, lugs, bezel, pendant, crown, bow, cap, and other parts thereof" (16 CFR 245.1(b)). The case back is the lid on the underside, which snaps or screws on and which a jeweler opens to change a battery. The case middle is the ring between front and back that carries the lugs for the strap.

Stainless steel is iron alloyed with enough chromium to resist rust. Most watch steel is a grade called 316L, covered in our guide to watch case materials. Base metal means any metal that is not precious, so steel, brass and zinc alloy are all base metals and a steel back is a base metal back too.

Plating is a thin coat of one metal laid over another, so a plated case can look like steel or gold while the metal under it is something else.

Where the phrase comes from

From 1968 the FTC had a set of rules for watches, the Guides for the Watch Industry, 16 CFR Part 245. Section 245.3 dealt with what a case is made of, and three parts of it explain the phrase.

1. Base metals, 245.3(j). A case or part that did not meet the gold or silver rules "should be marked as 'Base Metal' or so as to identify clearly the kind or kinds of metal of which they are composed". The examples were "Aluminum," "Stainless Steel" and "Chromium Plated Steel."
2. Combination of metals, 245.3(k). A case "composed of parts having different metallic compositions" should carry "an accompanying explanation of the part or parts to which such markings or descriptions apply". The examples were "Base Metal Back" and "14 K Gold Filled Bezel."
3. Placement, 245.3(m). The marks should be permanent, "made on the exterior, exposed surface of the back" and "stated in the English language".

Put the three together and you get the phrase: a case with a steel back and a different middle should name the metal, name the part, and say so on the outside of the back. "Stainless Steel Back" does all three in three words. The same section set the rules for gold filled and plated cases, which our answer on what gold filled means on a watch sets out.

The rule ended in 1999

The FTC rescinded the Watch Guides with effect from 9 June 1999 (64 FR 30898). On base metal marks, it found "it may not be necessary, to prevent deception, to advise that all non-precious metal watches be affirmatively marked". Its reason was that "a reasonable consumer is unlikely to assume, in the absence of any representation about the watch's metallic composition, that the watch was composed of a precious metal."

The notice also records who wanted the mark kept: Seiko, the American Watch Association and an EU committee said it "provides the consumer information about the watch". Timex wanted it dropped for watches under $100, and the Swiss watch federation said "the U.S. is the only country that requires marking of base metal watches".

The part-by-part idea did not go away with the guides, though. The FTC wrote that sellers "should know, without the Watch Guides, that they may need to qualify a mark indicating a watch's metallic composition, when that mark applies to only certain parts of a watch". That duty now rests on section 5 of the FTC Act, the general ban on deceptive claims, and the notice adds that objective claims about watches "must be truthful and accurate, and substantiated by competent and reliable evidence".

So no federal rule today makes a maker stamp "stainless steel back", but a plain "stainless steel" on a watch with a brass middle is the kind of mark the FTC said may need qualifying. Naming the back is the safe way to say it, which helps explain why the habit outlived the rule. The Swiss comment suggests the base metal mark was a US habit from the start.

What the rest of the case is made of

US Customs (CBP) issues rulings to importers that describe each watch metal by metal, and we read nine that describe a watch with a stainless steel back. Five name the metal of the rest of the case, and it is zinc alloy or brass every time. The other four give only a finish, a plating, or the words "alloy" or "base metal".

Nine rulings are not a survey of the market, since each describes one importer's own samples and letters, but they show what the phrase sits on in practice. Two details stand out. The plating in I87167 is three layers over zinc alloy, with a top coat about a tenth of a micron thick, and N183635 is the clearest case of the old pattern: one mark for the bezel, one for the back, both on the back.

One case back, read line by line

Take the back described in N183635, a 2011 ruling on a watch imported by M.Z. Berger. It reads "Base Metal Bezel", "Style GEN598", "Battery 377", "Japan Movement" and "Stainless Steel Back". Here is what each line tells a buyer, walked through from the ruling and the rules above rather than from any test of the watch.

1. "Stainless Steel Back". The lid is steel, and that is all this line covers.
2. "Base Metal Bezel". The ring on top is neither steel nor precious metal, which is 245.3(k) at work: a second mark for a second part.
3. The case middle. No line names it. The ruling calls it an "alloy watch case" with palladium nickel plating, which a buyer reading the back alone would never learn.
4. "Japan Movement". The movement was made in Japan, and under CBP practice that makes the whole watch Japanese, even though the ruling says the case and bracelet were made in China. Our answer on what Japan Movt means explains why.
5. "Battery 377". This is the cell to buy, and our answer on whether a 377 is the same as an SR626SW covers the numbers.
6. What is missing. Customs also wants the case's own country and the maker's or importer's name on the inside or outside of the back, under HTSUS chapter 91, Additional U.S. Note 4(c). The ruling does not quote those marks.

Read together, the back says steel lid, base metal bezel and Japanese movement, while the middle, the largest part of the case, goes unnamed.

What each metal mark on a back means

The second row is the useful contrast. In N165795, two GUESS cases were stainless steel, one of them gold plated. Both backs read "steel". The third case was brass, and its back read "stainless steel back". Same brand and same year, yet the wording followed the metal of each case. The second steel case also had "an ion plated base metal bezel", and its back still said only "steel". So a plain "steel" covers the case, not always every part on it. Wording such as "All stainless steel" claims the whole case in so many words.

How to tell what the rest of the case is

1. Read the whole back first. A second line such as "Base Metal Bezel" may answer the question, and if the back names only itself, assume the rest is not the same metal.
2. Do not rely on a magnet. Grade 316 steel is austenitic, made of a form of iron that "is nonmagnetic" when annealed, as Meyer Tool's materials note puts it. Its relative permeability is about 1.002 to 1.005, though cold working can make it slightly magnetic. So a magnet that does not stick tells you nothing, because a steel case would not hold it either.
3. Look where the finish wears. Edges lose a coating first, as our guide to case materials explains. Stainless steel is the same silver-grey all the way through, so if a yellow metal shows at a worn edge under a silver finish, that is not steel; brass is a yellow copper alloy. A pink or copper color can be an underlayer, like the copper coat in I87167. A coating can sit on steel too (one GUESS steel case was gold plated), so wear tells you about the finish first and the base second.
4. Read the listing. If a seller writes "stainless steel" and the back says "stainless steel back", ask what the case middle is, since the FTC's own words put that answer on the seller.

Why it matters

Skin. The back is the part that touches the wrist all day, and two rulings in the table describe the steel backs as "nickel free". That does not cover the rest: in N183635 the case and bracelet plating was 30 percent nickel. Plating also wears through at edges, so if a watch with a steel back still bothers your skin, our page on a watch that irritates the skin explains how to tell the cause.

Wear. The old US rules wanted coatings thick enough "to render lasting and effective service", unless the buyer was told otherwise (245.3(l)). That rule went with the rest in 1999, and the top coat in I87167 was 0.10 to 0.15 microns. How long a coat lasts depends on its thickness, and no mark on the back states it.

Value. The phrase does not tell you a watch is bad; it tells you which part is the steel one. Whether steel itself is the right choice is a separate question, taken up in is titanium better than steel.

Why both answers persist

"It means the watch is stainless steel" persists because the words "stainless steel" are the biggest on the back, and listings repeat them. It is wrong, because the mark names one part. "It means the watch is cheap" is closer, since the rulings show plated zinc alloy and brass under the phrase. But it overreaches, because the phrase is a description, not a grade, and a maker who names the back is being more precise than one who stamps nothing. Our guide to watch marketing claims covers similar phrases.

When this answer stops applying

• The watch was made for another market. Only US rules were read for this page. Other countries' marking rules may differ.
• The words are a seller's, not a maker's stamp. A listing that says "stainless steel back" may be copying the back or describing it loosely, and only the case itself can be checked.
• The back is gold or another precious metal. Precious metal marks follow other laws, which our answer on what 750 means on a watch covers.
• Nine rulings are a sample. They show what the phrase sat on for those importers, not what any one watch is made of, and a back mark can be false. Our guide to spotting a fake watch covers marks a case does not live up to.

Otherwise: "stainless steel back" means the back is steel and the rest is not. On the watches CBP described, the rest was plated zinc alloy or brass, or a base metal it did not name.