ISO 5753-1 — Radial internal clearance

Radial internal clearance is the total distance one ring can be moved relative to the other, radially, with the bearing under no external load. ISO 5753-1 gives the permitted range for that movement, split into groups. The groups matter because clearance is not a quality grade — it is a fit decision. An interference fit on the shaft expands the inner ring and consumes clearance, and a hot inner ring expands more than a cool outer ring, so a bearing that is correct on the bench can be tight in service.

The ranges are written as pairs: the lower figure is the minimum and the upper is the maximum. These are pre-mounting values for an unmounted bearing, measured without load or measurement forces. Fitting and temperature change them, and usually in one direction — downwards. This table runs on to a 315 mm bore, one bucket past the largest deep groove ball bearing here at 300 mm.

C2

Tighter than the default. Used where the fit already takes up most of the clearance, or where radial play must be kept small.

CN (normal)

The default. Usually not marked on the bearing at all — if the designation carries no clearance suffix, it is this group.

C3

Looser than the default. The common choice for interference fits on the shaft, for electric motors, and wherever the inner ring runs hotter than the outer ring.

C4

Looser again. For heavy interference fits and high-temperature service, where thermal expansion would otherwise close the fit up.

C5

The loosest group in the table. Special applications only.

A table of its own, not a slice of the one above. The two are laid out identically and agree over the bores they share, and a row taken from the wrong one is still a well-formed row — but at a 20 mm bore the groove ball table allows 5 to 20 µm in CN where this table allows 10 to 23 µm. Read the heading, not the shape of the row. This table stops at a 100 mm bore, the largest bore in the self-aligning ball family this library carries. The standard continues past it.

Five groups. Two separate things decide where the table ends, and neither of them is where the standard ends. The first is this library's cylindrical roller family, which all 55 designations here run from 20 to 95 mm — the standard carries the same table on to a 500 mm bore. The second is the source rule: above a 100 mm bore only one of the sources this library checks gives the C2 and C5 columns, and a figure that cannot be checked against a second independent source is not published here at all, so the table ends where two sources still agree on every column. The values also run much looser than the ball tables: at a 30 mm bore this table allows 20 to 45 µm in CN where the groove ball table allows 5 to 20 µm. This table runs on to a 100 mm bore, one bucket past the largest cylindrical roller bearing here at 95 mm.

This is the cylindrical bore table. That distinction matters here and nowhere else on this page: ISO 5753-1 gives this bearing type a second table for tapered bores, and the two do not agree. A 22320 EK, whose suffix K means a 1:12 tapered bore, is tabulated in the tapered-bore table with values that differ from these in every group — checking this table against that bearing's data would read as a conflict between sources when the two tables are simply describing different bores. Every designation in this library has a cylindrical bore, so the tapered-bore table is left out rather than printed against bearings that do not exist. The values sit well above the ball tables: at a 30 mm bore this table allows 25 to 40 µm in CN where the groove ball table allows 5 to 20 µm. This table stops at a 100 mm bore, the largest bore in the spherical roller family this library carries. The standard carries it further.

Read down any row and the top of one group sits above the bottom of the next: in the groove ball table at a 20 mm bore the CN range starts at 5 µm while C2 reaches 10 µm, and in the self-aligning table the same two groups overlap at 10 µm and 14 µm. That overlap is how the standard is written. It looks like a mistake to anyone who expects the groups to partition the range, and writing them out as non-overlapping would mean changing the values to make a tidier table.

ISO 5753-1 gives clearance values for six bearing types — radial contact groove ball bearings, double-row self-aligning ball bearings, cylindrical roller bearings, needle roller bearings, toroidal roller bearings and double-row self-aligning roller bearings — with cylindrical bore, plus tapered bore for four of them. Each type has its own table, and the numbers differ between them. Four of the six are reproduced above — deep groove ball, self-aligning ball, cylindrical roller and spherical roller — one table to each type this library carries designations for. The remaining two — needle roller and toroidal roller — have no table here. The needle roller bearing has designations on these pages and no clearance table: the catalogues consulted contradict each other on its values, so none is reproduced. The toroidal roller bearing carries no designation here at all. Comparing a figure here with one quoted for a needle roller bearing in a maker's catalogue will not agree, and the discrepancy is in the two tables being different, not in either being wrong.

Four of the six types — including the self-aligning ball bearing — also have a tapered bore table in this standard, for designations that carry a K suffix. Every designation in this library has a cylindrical bore, so a tapered bore row has nothing here to be the clearance of, and the tables are left out rather than printed against bearings that do not exist. A 1204 K is a real bearing; it is simply not one of the ones catalogued here.