Almost every ANSI roller chain carries its size stamped directly on the outer link plate, and the digits encode pitch, type, and strand count in a fixed format that has not changed in decades [S5]. A reading of "40-2" on a chain is shorthand for a 1/2-inch (12.70 mm) pitch standard series duplex chain; the same chain could equally be called "#40-2" or "40B-2" depending on which standard the manufacturer follows, but the geometry is identical [S2][S3].
The most common stamped pattern on a drive chain is a number, an optional letter, and an optional strand suffix, in that order. Knowing how to parse each component prevents ordering the wrong replacement, especially when the chain has been degreased, painted, or partially worn [S4][S5]. For broader context on the roller chain family and how it sits next to other power-transmission elements, the numbering system described here is the same one used across ANSI single-strand, duplex, triplex, and heavy-series product lines.
Anatomy of a Stamped Chain Number: Pitch, Type, Strand
The first one or two digits of an ANSI chain number denote pitch in eighths of an inch, so "#40" means 4/8 inch = 0.500 inch (12.70 mm), "#60" means 6/8 inch = 0.750 inch (19.05 mm), and "#80" means 1.000 inch (25.40 mm) [S3][S4]. This convention covers the full ANSI B29.1 range from #25 (1/4 inch / 6.35 mm pitch) up to #240 (3 inch / 76.20 mm pitch), with thirteen standard sizes in between [S3].
The last digit of the chain number is a type code, not part of the pitch. A trailing "0" marks a standard roller chain, which is the default for sizes #40 through #240 [S3]. A trailing "5", as on #25 and #35, indicates a bushing chain where the roller position is filled by a plain bushing rather than a free-rolling roller, so ASME B29.1 lists a bushing diameter instead of a roller diameter for those two sizes [S3]. A trailing "1", as on #41, marks a lightweight riveted-pin chain that shares #40's 1/2-inch pitch but drops the separate bushing; it is not a drop-in substitute for #40 [S3][S4].
After the chain number, a strand suffix tells you how many parallel rows of chain run side by side: "-1" is single strand (often omitted), "-2" is duplex, "-3" is triplex, and so on [S2][S3]. A "60-2" mark, for example, specifies a 3/4-inch pitch duplex chain that needs a wider duplex-matching sprocket rather than a single-strand #60 sprocket [S2].
Heavy Series, Stainless, and Brand Suffixes: What "H" and Maker Marks Mean
Heavy series chains carry an "H" suffix after the size, written as "60H" or "80H", and the same convention applies to duplex versions such as "60H-2" or "80H-3" [S7]. The H designation keeps pitch and roller diameter identical to the standard chain but uses thicker link plates for higher tensile strength and shock-load capacity; for example, ANSI heavy roller chain #60H-1 has the same 0.750-inch pitch as #60-1 but with thicker side plates [S7]. The H suffix is the most common non-numeric stamp on a working drive chain, and it is what a maintenance technician is most likely to see on a mining, forestry, or aggregate-duty drive.
Manufacturer and grade stamps are layered on top of the ANSI number and follow a separate logic. Standard ANSI chain typically carries no additional letter mark beyond the size; higher-grade chains are stamped with letters, symbols, or brand codes indicating the manufacturer's specification tier [S4]. Premium or "super premium" chains, stainless-steel chains, nickel-plated chains, and coated chains (for example nitrile- or zinc-coated) are usually identified by a brand mark plus the same ANSI size code, so the side plate might read "XYZ 40-1" or "40-1 SS" depending on maker convention [S5]. When a chain has been re-stamped by a distributor, the brand letter can disappear, leaving only the size, which is why reading the size stamp correctly is the foundational skill [S4].
Step-by-Step: Reading the Stamp and Cross-Checking With Calipers
The fastest path to identification is a clean visual read on the outer plate. Wipe the side plate with a rag or a mild solvent, then read the stamp with a flashlight at a low angle; grease, paint, and surface rust are the three reasons a real "#60-2" mark can look like a worn blank [S5][S6]. When the stamp is legible, the chain is identified and no further measurement is needed beyond matching the sprocket tooth count and bore to the application [S1][S3].
When the stamp is gone, four caliper measurements will get you back to the same answer, and pitch is the dominant one. Measure the center-to-center distance between two adjacent pins across ten pitches, then divide by ten; spreading the measurement out averages single-pitch manufacturing variation and any in-service stretch down to a value accurate within roughly ±0.01 mm on a typical digital caliper, which is well inside the 3.175 mm (1/8 inch) gap between consecutive ANSI sizes [S3][S4]. The other three cross-checks are roller (or bushing) diameter measured across the outside of the roller at its widest point, width between inner plates measured at the inner link where the sprocket tooth sits, and pin diameter measured through the plate hole; small differences such as 0.156 inch pin for #40 versus 0.141 inch pin for #41 are what separate chains that share the same pitch but are not interchangeable [S1][S3].
For a quick worked example, a #40-1 single-strand chain should measure 0.500 inch pitch, 0.312 inch roller diameter, 0.312 inch width between inner plates, 0.156 inch pin diameter, 0.058 inch plate thickness, and 3,970 lbf minimum ultimate tensile strength per the USA Roller Chain single-strand table [S1]. A #60-1 should read 0.750 inch pitch, 0.469 inch roller diameter, 0.500 inch inner width, 0.234 inch pin diameter, 0.093 inch plate thickness, and 9,270 lbf tensile strength; if your calipers return those numbers, the side-plate stamp was "60" or "60-1" [S1].
Pitch vs. Width: Why Three Chains at 1/2-Inch Pitch Are Not Interchangeable
Pitch alone does not pick a chain, because #40, #41, and metric 08B all share 0.500 inch (12.70 mm) pitch and will physically sit on a sprocket cut for any of them, but only one is the correct match for a given sprocket and duty [S3]. The disambiguators are roller diameter, inner width, and pin diameter, plus plate configuration; pin diameter is often the single tightest tolerance, and a chain that rides the sprocket but has the wrong pin will fail at the pin or the plate hole long before it reaches its rated tensile load [S3][S4].
The table below lines the three 1/2-inch-pitch options up against the criteria a maintenance engineer would actually use to choose between them, drawn from the ANSI B29.1 figures published in current sizing references.
For drives that need more torque than a single-strand chain can deliver at a given pitch, the duplex or triplex suffix is the way to scale up without changing sprocket geometry: a "#40-2" duplex fits the same 0.500-inch pitch sprocket family as "#40-1" but carries load across two parallel strands, and a "#40-3" adds a third row for high-torque, low-speed service such as heavy machinery drives [S2][S3]. The trade-off is wider overall chain width and a sprocket specifically cut for the strand count, since a single-strand sprocket will not engage a duplex chain correctly.
Wear, Stretch, and When the Stamp Is No Longer Trustworthy
Roller chain stretches in service, and that stretch is what eventually makes the stamp-on-the-side-plate identification unreliable as a stand-alone method. ANSI/ISO practice is to measure pitch across multiple links under the chain's rated measuring load; a single-pitch measurement on a worn chain will read long because the pins and bushings have already elongated, and that false reading will push you to order the next size up [S3]. The fix is the ten-pitch averaging method described above, which gives a true pitch reading independent of single-link wear [S3][S4].
At the wear limit, most maintenance standards call for chain replacement once elongation reaches roughly 3% over the original pitch; beyond that, the chain no longer sits correctly in the sprocket tooth profile, tooth jumping and accelerated sprocket wear follow quickly, and the side-plate stamp becomes academic because the chain should be scrapped rather than reused [S3][S8]. The other reason a stamp goes unreadable is surface damage, not wear: a stamped "#50-2" can be lost to grinding, shot-blasting, heavy paint, or decades of grease mixed with iron oxide, and the only path back to identification at that point is the four-measurement caliper routine [S5][S6].
Common Mistakes When Decoding a Chain Stamp
The single most common error is reading a "#60H" as a "#60" and ordering a standard plate chain in place of a heavy-series one; the chains have the same pitch and roller diameter, so the new chain will fit the existing sprocket, but it will run at a lower tensile rating and a shorter fatigue life, especially under shock load [S7]. The reverse error, reading a "#60" as a "#60H" and over-specifying, is harmless to the drive but costs money in chain and sprocket price; the dangerous direction is under-specifying, which is why any chain whose duty cycle includes shock loading should be checked for the H suffix before the replacement is ordered [S7].
The second most common error is strand-count confusion. A duplex chain stamp that has lost its "-2" suffix (or was never marked clearly) is sometimes ordered as a single-strand #40, and the resulting drive either will not close at the master link or will run on a single-strand sprocket with the second row hanging in space [S2]. The quick visual check is to look at the chain from the end: one row of link plates is single-strand, two parallel rows is duplex, three is triplex, and the strand count is rarely ambiguous once the chain is clean [S2][S3].
The third error is mixing ANSI and metric ISO chains. A chain stamped "08B" is a 12.70 mm pitch ISO 606 chain, dimensionally close to ANSI #40 but with different roller, width, and pin dimensions, and it will not run on a true ANSI #40 sprocket without accelerated wear [S3]. For facilities that run both ANSI and ISO equipment, the safest practice is to keep a small set of go/no-go plug gauges keyed to the four ANSI dimensions, and to physically check any chain whose stamp is missing the ANSI "#" prefix or carries an "B" suffix against the gauge before installation [S3][S4].
Standards, Sources, and Sourcing Signals
The governing document for ANSI roller chain dimensions is ASME B29.1-2011, which specifies the 14 standard sizes from #25 through #240 plus the four heavy-series variants; every measurement described in this article (pitch, roller diameter, inner width, pin diameter, plate thickness, and minimum tensile strength) is taken directly from that standard as published in current manufacturer and distributor reference tables [S3]. For ISO metric chain, the equivalent is ISO 606, which uses an "B" suffix in the chain number and dimensions in millimetres [S3]. When the side-plate stamp references either system, the standard is fixed and the dimensions are not negotiable, which is why a measured pitch of 12.70 mm plus a measured pin diameter of 4.45 mm is unambiguously "08B" and not "#40" [S3].
For engineering teams sourcing replacement chain by stamp alone, two signals are worth tracking on an ongoing basis. First, the broader tapered roller bearing and roller bearing market is a useful proxy for steel price and heat-treated plate availability, since both bearing and chain use through-hardened alloy steel and the same mill lead times; sustained rises in bearing lead time tend to precede chain lead-time extensions by a quarter or two. Second, the roller conveyor segment is a useful demand signal for attachment chain and hollow-pin chain, both of which use the same ANSI number system described here and frequently share inventory with drive chain at the distributor level; if conveyor OEMs are running extended lead times, attachment chain stock at the same pitch is often the next thing to tighten.
This topic is covered further in Rail, carriage, end cap, end seal, and retainer roles in a linear guide.