Have you ever wondered where and how roller chains get their identifying numbers? This is a very common question we are asked, so we're covering it! This article explains the ANSI (American National Standards Institute) roller chain numbering systems, detailing how numbers are determined for ANSI sizes from #25 to #240.
The ANSI Roller Chain Numbering System
The ANSI standard, governed by ASME/ANSI B29.1, set number and dimensional standards for several primary roller chain sizes for power transmission. The numbering system indicates the chain pitch—the distance between roller centers—in eighths of an inch (1/8 or 0.125 inch increments). The first digit(s) (excluding the last digit) of a chain number represents the number of eighths of an inch in the pitch. To determine the pitch, multiply the first digit(s) (excluding the last digit) by 0.125" inches (or 1/8 inch), or equivalently, divide by 8.
Example Chains
- #40: 4 × 0.125" = 0.500" pitch
- #100: 10 × 0.125" = 1.250" pitch
- #240: 24 × 0.125" = 3.000" pitch
The last digit indicates the chain type:
- 0: Standard roller chain (with rollers).
- 1: Lightweight chain (e.g., #41 is a narrower, lighter version of #40).
- 5: Bushed chain (rollerless, with bushings instead of rollers).
The suffix letters:
The only suffix letter recognized by the ANSI standards is "H" that denotes a heavy-series roller chains with thicker plates for increased strength (e.g., #60H). There are many other suffix's designations used by companies that have specific meanings, which is covered below under Roller Chain Nomenclature.
Here is a table of all ANSI sizes from #25 to #240 with their pitches:
| ANSI Size | Pitch (inches) | Type |
|---|---|---|
| #25 | 0.250 | Bushed (rollerless) |
| #35 | 0.375 | Bushed (rollerless) |
| #41 | 0.500 | Lightweight |
| #40 | 0.500 | Standard |
| #50 | 0.625 | Standard |
| #60 | 0.750 | Standard |
| #80 | 1.000 | Standard |
| #100 | 1.250 | Standard |
| #120 | 1.500 | Standard |
| #140 | 1.750 | Standard |
| #160 | 2.000 | Standard |
| #180 | 2.250 | Standard |
| #200 | 2.500 | Standard |
| #240 | 3.000 | Standard |
Roller Chain Nomenclature: Variations Among Manufacturers
While the ANSI standards provide a foundational numbering system for roller chains, nomenclature can vary significantly among different manufacturers. These variations extend beyond the basic chain numbers and include additional designations for materials, construction types, special features, coatings, and performance enhancements. This diversity in terminology can make it challenging to compare products or ensure compatibility when sourcing from multiple suppliers. We offer a full detailed explanation of the Nitro Chain Nomenclatures that breakdown our item numbers for different styles of roller chain.
