Key takeaways
- ISO 6194 is the common reference. JIS B2402 and the current DIN version are both harmonised with it, so the dimension series and the tolerance rules match.
- DIN 3760 is the designation familiar from old drawings. The version in force is DIN ISO 6194, so citing DIN 3760 in new documentation is citing a document that has been replaced.
- What really differs between the systems is how the seal type is NAMED, not the dimensions. TC, TB and SC are trade conventions, and no standards system issues those letters.
- In technical documentation, write the dimensions and the material first and the standard designation after. No standard backs the letter part of a trade code.
A plant runs Japanese equipment, works from drawings issued by the parent company in Germany, and has a local supplier citing ISO in its quotation. Three designations, and the practical question is always: is this the same part, and which number goes in the documentation.
ISO 6194 is the reference system
ISO 6194 specifies rotary shaft seals with an elastomeric lip: the dimension series, the tolerances, the designation format and the test methods.
Both JIS B2402 and the current DIN version are harmonised with it. That is why a seal for a 25 mm shaft bought in Japan, in Germany or in Vietnam is 25 x 47 x 7 and interchangeable.
In other words: on the numbers, the three systems have converged. The argument about which one to cite is largely an argument about the form of the documentation, not about the part.
DIN 3760 is a designation that has been replaced
This is the point that most often gets contested in approval documentation.
DIN 3760 is the familiar German designation and it still appears on old drawings, in old spare parts lists and in the everyday speech of engineers. But the version in force is DIN ISO 6194, the DIN adoption of the ISO standard.
The practical consequence: citing DIN 3760 in new documentation is citing a document that has been superseded, and the reviewer is entitled to ask for a correction. On old drawings leave it as it stands, but when issuing new documents write the designation currently in force.
Where the three systems really differ is in naming the seal type
The numbers have converged. The letters have not, and no system issues those letters.
TC, TB, SC and TA are trade conventions shared by Japanese and Taiwanese manufacturers. The whole market reads them the same way, so in practice they are a common language, but no standard defines them.
The consequence for the documentation: a line reading "TC 25 47 7 to JIS B2402" mixes two reference systems. JIS backs the "25 47 7" part; it does not back the "TC" part.
A tighter way to write it is to describe the attributes rather than rely on a trade code: dimensions, case type, number of lips, spring or no spring, lip material, working temperature range.
Tolerance class is worth reading closely
A matching dimension series does not mean matching tolerances at every class.
Two parameters decide the fit:
- Outer diameter tolerance decides the interference when the seal is pressed into the housing bore. Too little and the seal turns in the bore; too much and the case distorts and the lip goes out of round.
- Thickness tolerance decides whether the seal seats fully in the bore to the correct depth.
When two sources declare the same dimension series but different tolerance classes, that is the point to record as "verify before use" in the cross reference table.
Which designation to cite in the documentation
The order should be: dimensions, material, construction attributes, and only then the standard designation. The standard designation comes last because it is the basis, not the description.
If the parent company requires its own system, write both: their designation and the corresponding ISO designation. Two lines, no contradiction between them, and one round of questions avoided when the documentation passes to another department.
Read next: cross-referencing OEM part numbers to a local source and choosing a material by the medium.
