In ISO/ABMA metric bearing nomenclature, a four-digit basic number packs three facts: type, dimension series, and bore, with suffixes handling tolerance, clearance, and seals [S1][S3][S4].
First digit selects the bearing family (6 = single-row deep groove, 3 = double-row angular contact, 5 = thrust ball); second digit picks the dimension series from the same family; the trailing two digits encode the bore, multiplied by 5 mm for codes 04 and larger, or read directly for 00/01/02/03 (4 mm to 9 mm) [S2][S4].
Anatomy of a Four-Digit Basic Number
Take 6206 as the worked example. The first digit 6 is the type code for a single-row deep groove ball bearing, by far the most common metric series in general machinery [S1][S2].
The second digit 2 is the dimension series within the 6 family: 6 0 = extra-light (61800 line), 6 1 = extra-light (61900 line), 6 2 = light, 6 3 = medium, 6 4 = heavy. A 6206 is therefore a light-series 6-type, and a 6306 of the same bore has a larger outer diameter and higher load rating because the 3-series carries more cross-section [S1][S3].
The last two digits 06 resolve as 06 × 5 = 30 mm bore, the rule that covers all metric codes from 04 (20 mm) upward. Codes 00, 01, 02, 03 are read as direct bore values: 10 mm, 12 mm, 15 mm, 17 mm [S2][S4].
Type Codes and Series Across the Catalog
Type codes 1 through 9 and the letter-prefixed families cover the full bearing range: 1 = self-aligning ball, 2 = spherical roller, 3 = double-row angular contact, 4 = double-row ball, 5 = thrust ball, 6 = single-row deep groove, 7 = single-row angular contact, 8 = felt-sealed ball; prefixed codes include R for inch, N for cylindrical roller, NN for double-row cylindrical, NA for needle, and QJ for four-point contact [S1][S2].
Thrust bearings use their own type field 5 with a sub-family: 51 and 53 are single-direction thrust ball, 52 and 54 are double-direction thrust ball, so a 51106 and 51210 are not interchangeable [S1][S7].
The dimension series (second digit) follows ISO 15 geometry, not just one number: for a 6-type deep-groove bearing, comparing 6204 (20 mm bore, 47 mm OD, 14 mm width, 1000 kgf dynamic) to 6304 (20 mm bore, 52 mm OD, 15 mm width, 1250 kgf dynamic) at the same bore shows the 3-series step adds OD, width, and roughly 25% dynamic load capacity [S1][S5].
Reading Bore, OD, and Width from the Code
Bore follows the multiplicative rule: code 04 = 20 mm, 05 = 25 mm, 08 = 40 mm, 12 = 60 mm, 20 = 100 mm; below that, 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm. Codes above 03 always mean bore = code × 5 mm [S2][S4].
Outer diameter and width are not encoded in the basic number, they come from the dimension series table. The 6 0 2 5 (6205) and 6 3 0 5 (6305) examples both have a 25 mm bore, but OD jumps from 52 mm to 62 mm and width from 15 mm to 17 mm, a textbook case of the 2-series vs 3-series trade-off [S5].
For a 6200, OD is 30 mm; for a 6000 of the same 10 mm bore, OD drops to 26 mm and width to 8 mm, with the dynamic load rating falling from 400 kgf to 360 kgf because the 0-series is the extra-light section [S5].
Suffixes: Tolerance, Clearance, and Seals
C3 means radial internal clearance greater than the Normal class, C2 and C4 bracket it on the tight and loose side; P5 (ABEC 5) and P6 (ABEC 6) are tolerance classes above Normal, while P0 (or no suffix) is Normal class per ISO 492 [S1][S3][S4].
Common seal codes follow: 2RS = rubber seals both sides, ZZ or 2Z = metal shields both sides, LLB = low-friction contact seal (NTN-specific), and so on. Suffixes are the most brand-dependent part of the code, so cross-reference is mandatory when a 6206 2RS from one maker has to swap into another maker's drawing [S2][S4].
Material and temperature prefixes matter for hot or corrosive service: TS2 = stabilized to 160 °C, TS3 = 200 °C, TS4 = 250 °C, 5S = ceramic rolling elements, F = martensitic stainless (440C equivalent), and no symbol typically means through-hardened AISI E52100 [S2].
Worked Decode Walkthroughs
6206: 6 = single-row deep groove, 2 = light dimension series, 06 = 30 mm bore; complete dimensions 30 × 62 × 16 mm, dynamic load 1530 kgf, static 1050 kgf [S5].
6309: 6 = single-row deep groove, 3 = medium series, 09 = 45 mm bore; dimensions 45 × 100 × 25 mm, dynamic 4150 kgf, static 3100 kgf; the 3-series step adds 23% OD, 32% width, and 87% dynamic capacity versus a 6209 of the same bore (2570 kgf dynamic) [S5].
6205-2RS-C3: a 25 mm bore light-series deep groove with rubber seals on both sides and a C3 internal clearance, a common electric-motor and pump-shaft spec; 25 × 52 × 15 mm, 1100 kgf dynamic [S2][S4][S5].
Common Mistakes and Limits of the Code
The four-digit basic number does not encode the load rating, the limiting speed, the seal material, the cage type, or the grease fill, all of which live in the suffix string or the manufacturer's datasheet. Assuming 6206 and 6206-2RS-C3 share a load rating is wrong: the seal and clearance change the speed limit and break the ISO 492 tolerance by definition, even though the bore and OD are identical [S1][S3][S5].
Inch codes, denoted with an R prefix (R10, R20), do not follow the multiply-by-5 rule; the bore is read in sixteenths of an inch or via the ABMA inch series tables, and trying to apply the metric decode to an R-series number is a frequent error when a metric drawing is cross-referenced against an inch-spec'd replacement [S2][S7].
For applications where the load is dominated by thrust, the radial-only deep-groove 6-type is the wrong family, an angular contact 7-type or a thrust ball 5-type is the correct geometry, and reading 5 11 06 vs 5 12 06 vs 5 13 06 from the same bore lets the engineer pick single- vs double-direction thrust correctly [S1][S7].
Interchange, Cross-Reference, and Standards
ISO 15 defines the dimension series and boundary dimensions, ISO 492 covers the tolerance classes (Normal, P6, P5, P4), and ABEC 1-7 grades are the US equivalent read alongside the ISO classes; ABEC 5 and P5 are equivalent in geometric tolerance, not in noise or life testing, a common over-simplification in distributor catalogs [S1][S3][S5].
Most premium makers (SKF, FAG, NTN, NSK, Koyo, Timken) publish cross-reference tables that map a competitor's 6206-2RS-C3 to their own suffix string, and the first step in any replacement decision is to verify the four-digit basic number plus the tolerance class plus the clearance class line up before anything else [S1][S2][S7].
For paired bearings in an O or X arrangement, suffix DB, DF, or DT marks the matched set, and a single 7206 is never a substitute for a paired 7206-DB without a redraw, the dimension series decodes the same, but the preload and load line are different [S2][S4]. When a design moves from a deep-groove 6-type to a different rolling element for higher stiffness or speed, the ball screw or ball spline catalogs on this site use the same ISO 15 dimension conventions, so the decode skill transfers directly.
Trackable signals: NSK, SKF, and NTN publish updated suffix decoding tables in their technical bulletins each year, and any change in ISO 15 dimension series additions (new bores, new OD steps) would land in those bulletins first. The next revision of ISO 492 tolerance classes is the spec to watch when a drawing calls for P4 or tighter; cross-check the latest catalog edition before ordering [S1][S3][S5].
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