Which Radial Internal Clearance Group and µm Range to Write on a Bearing Drawing

The µm range you write is an unmounted, zero-load value

The clearance figures published in catalogue tables are defined for an unmounted bearing under zero measuring load¹. That is a bench condition, not a running condition.

Once the bearing is pressed onto an interference shaft and the inner ring runs hotter than the outer, the running clearance is smaller than the number you copied onto the drawing. So the tabulated value is a starting point.

Treat the drawing range as the unmounted base value and fix the group with the fit and the ring temperature difference in mind before you release the specification¹. Writing the catalogue number straight onto the drawing as if it were the operating clearance is the error this step exists to prevent.

One limit applies to the whole article: no source in this set reproduces the per-bore minimum and maximum µm values for each group. You will take those numbers from the governing table for your bearing, not from here.

Which standard governs the numbers for your bearing type

ISO 5753-1:2009 is the table cited for metric radial clearance, and the values are valid for unmounted bearings under zero measuring load¹. It is not universal.

Metric and inch deep groove ball bearings follow different standards, ISO and domestic cylindrical roller bearings differ, and straight-bore and tapered-bore values are not the same¹⁵. Tapered roller bearings sit outside the radial system altogether.

No standard radial clearance table exists for them; clearance is expressed axially as bench end play and set per application¹⁵. If your drawing is for a Tapered Roller Bearings part, a radial µm range is the wrong unit.

Before you trust a catalogue column, ask the supplier which standard and which edition the printed values follow for your exact bearing type and bore. The sources do not establish that any particular supplier's catalogue matches ISO 5753 for your size.

Choosing the group from fit and ring temperature

Interference fits and a hot inner ring both eat clearance, and both push the choice toward a looser group. The direction is consistent across the sources; the recommended group is not, because it depends on bearing type and how severe the condition is.

For cylindrical roller bearings the picture inverts. They carry heavier radial loads, so they need tighter shaft and housing fits and start with higher initial clearance, and CN is usually preferred over C3 to absorb the post-mount reduction¹⁰.

A Cylindrical Roller Bearings specification that defaults to C3 without checking the fit is not following this guidance. Where the inner ring runs hotter than the outer, a clearance larger than Normal, C3, is the recommended direction¹¹.

One supplier describes C3 as the default for many common industrial motors and gearboxes, with C4 as the next step when C3 is insufficient for exceptionally high temperature or a large shaft-to-housing thermal differential¹². What none of this gives you is a number.

No source quantifies the µm lost to a given fit or a given ring section, so you cannot compute the correction from these pages. Ask the supplier to state the expected clearance reduction for your fit and temperature case.

Matching the operating condition to a candidate group

Use this as a first pass to name a candidate group, then test it against the fit and ΔT reasoning above. The condition-to-group mapping comes from one supplier's selection table¹⁹ plus a second supplier's C3/C4 guidance¹²; neither is a governing limit.

Narrowed and special ranges

The standard band is not the only option. One supplier offers C2H, the upper range of C2, specifically to reduce noise levels further¹⁰.

That is a supplier position, not an industry rule, and it tells you a narrowed range can be requested where quiet running is the driver. A narrower band costs you selection freedom at the supplier.

Whether it costs money, adds lead time or carries a minimum order is not stated anywhere in this evidence. Ask for the premium and the availability of the narrowed range alongside the standard group when you send the RFQ, and compare the two answers rather than assuming the special range is stocked.

For a Deep Groove Ball Bearings drawing where noise is the governing requirement, C2H is worth naming as an alternative to plain C2.

Verifying the clearance by the right method

The measurement method has to match the bearing type, or the certificate will describe something other than what you specified.

• ✓For small ball and cylindrical roller bearings, confirm the supplier measures radial clearance with a dial indicator, one race fixed and the other push-pulled 180°.
• ✓Do not demand a radial dial-indicator certificate for large, heavy industrial bearings; that method does not suit them.
• ✓For tapered roller bearings, specify and verify axial bench end play instead of a radial figure.
• ✓For tapered-bore spherical roller bearings, confirm the clearance is checked with a feeler gauge before and during drive-up on the taper.
• ✓Ask the supplier to state on the certificate that values refer to an unmounted bearing under zero measuring load.

Where the sources disagree on the preferred group

The disagreement is narrower than it looks: it is about which bearing type and condition each recommendation was written for, not about the physics. Both sides stay visible below so you can see which one matches your case.

Before you request a quote

• The evidence leaves this open — put it to the supplier: no source in this set reproduces the per-bore minimum and maximum radial clearance in µm for each group, so the numerical range on the drawing must come from the governing table for your bearing, not from this article.
• The evidence leaves this open — put it to the supplier: no quantified clearance-reduction formula or coefficient as a function of fit and ring section is given; ask the supplier what reduction to expect for your interference fit.
• The evidence leaves this open — put it to the supplier: no clearance-change-per-ΔT coefficient or formula is given; ask the supplier how much clearance your ring temperature difference will consume.
• The evidence leaves this open — put it to the supplier: no DIN 620 or ABMA table values and no regional deviation data are established; confirm which standard and edition the supplier's catalogue follows.
• Request a written quote with price basis, MOQ, tooling, payment terms and production lead time.
• Request certificate numbers, issuing bodies, scope and validity for the exact model and destination market.
• The evidence leaves this open — put it to the supplier: no data on half-group or matched-set narrowed ranges beyond the C2H mention, and no cost for them; ask what narrowed ranges the supplier can offer for your bore.