What a Bearing RFQ Must Contain for an Accurate Quote

Can you quote from the part number alone?

A bearing designation is dense, but it is not self-verifying. A standard number encodes the bearing type, the dimension series and the bore code, plus prefixes and suffixes for cage, sealing, clearance and precision class^13,14.

That is the most information-dense field you can put in an RFQ. The catch is the bore code: it is a multiplication, so 05 means 25 mm bore^13,14 (supplier-reported figure).

Small bearings under 20 mm bore use the special codes 00, 01, 02 and 03 for 10, 12, 15 and 17 mm, and bearings of 500 mm bore or larger state the actual bore size directly¹⁴ (supplier-reported figure). Get the code wrong and the supplier quotes a different part.

The series is the second trap. At the same 20 mm bore, the 6004, 6204 and 6304 sit at 42 mm, 47 mm and 52 mm outside diameter¹³ (supplier-reported).

So a 6205 and a 6305 share a 25 mm bore but not an outside diameter, and a quote built on part-number similarity alone is not safe¹⁶ (supplier-reported).

Bore, outside diameter and width are the three critical dimensions, and substitution is only safe when those three match along with clearance designation, sealing configuration, cage material for demanding conditions, precision class and every other technical specification¹⁶.

If your RFQ carries the full designation and the three dimensions, the supplier can verify rather than assume. Write the bore, OD and width on the RFQ even when the part number is legible.

State the conditions that fix clearance and precision

Clearance, precision class and seal suffix are not free choices. They are outputs of the operating conditions, so an RFQ that omits those conditions forces the supplier to guess.

Internal clearance has no universally best class; it has to be matched to operating temperature, shaft fit, speed, load and precision requirements¹⁷.

A bearing running hot with an interference shaft fit needs a different clearance class than the same bearing in a cool, loose-fit application, and the RFQ cannot get the class right without stating temperature, fit and speed¹⁷. Precision follows the same logic.

Selection should start from the application's actual speed and runout needs rather than a catalog default, and one source maps speed bands to classes — under 3,000 rpm to ABEC 1, 10,000–30,000 rpm to ABEC 5, above 80,000 rpm to ABEC 9¹⁹.

The cost gap is real: one source reports ABEC 7 and ABEC 9 bearings cost 5–10× more than ABEC 1 equivalents of the same bore and series¹⁹. Sealing is the third output.

Open bearings suit only a controlled lubrication system; otherwise 2RS or ZZ should be chosen on the dust, moisture and speed profile²¹. Load must be quantified as actual radial and axial forces including belt tension and gear mesh force, not static weight^3,21.

If your RFQ states temperature, fit, speed, load direction and the dust or moisture environment, the supplier can propose the clearance, class and suffix instead of guessing. Put those five conditions in the RFQ body, not in a note.

Which bearing type should the RFQ ask for?

Load and speed pull in opposite directions, and the RFQ has to say which one the application needs.

Roller bearings generally carry higher loads for a given bore and outside diameter because line contact spreads stress over more area, while ball bearings run faster and quieter because point contact generates less friction and heat at speed¹². Within ball bearings the split is just as sharp.

A deep groove bearing accepts axial load in both directions at a lower contact angle and suits a case where high speed is not required, whereas an angular contact bearing is the choice when high operating speed, guidance of rotating parts and high rigidity are required^7,20.

One source reports deep groove bearings carry axial load at roughly 25–35% of the static radial rating, so axial duty is a real constraint on type choice⁹. These types are not interchangeable, so the RFQ should name the type or give the load and speed that determine it.

If your application is a high-speed spindle, say so — the supplier will quote angular contact, not the cheaper deep groove part.

Write quantity, brand and documentation clauses

Price is not decided by bearing type alone. It depends on material, precision grade, size, structure, sealing design, cage material, heat treatment, manufacturing difficulty, brand, order quantity and application requirements together²³.

An RFQ that leaves brand or quantity open returns quotes you cannot line up against each other. Suppliers themselves ask for the bearing model, drawing, quantity or application details before they quote, and one states a 24-hour quotation response once those fields are present^10,27.

That is a single supplier's claim, not an industry rule, but it shows what the practical minimum looks like. Documentation is the clause buyers most often forget.

Buyers are told to demand ISO 9001 certification and Material Test Reports confirming steel cleanliness and alloy composition, with ATEX or RoHS documentation where the environment requires it¹¹. For critical-path motors above 200 HP, quality control should extend to 100% vibration and noise testing at the factory, often documented via Anderometer readings¹¹.

The highest precision grades are individually serialized and often sold with inspection certificates showing measured rather than nominal class values²². In medical and aerospace work, buyers continue to specify established precision manufacturers regardless of unit cost, so the RFQ must state the approved-vendor constraint²⁸.

Write the quantity, the acceptable brand or manufacturer pool, and the certificate list as separate lines. If your motor is on a critical path, name the vibration test in the RFQ — it is not implied by the part number.

Check the RFQ before it goes out

Every missing field becomes a round trip. No quantity means no price break and no comparable quote.

No brand constraint means an unapproved part arrives. No documentation clause means certificates cannot be obtained after the order.

No delivery date means the lead time quoted is the supplier's default rather than your need. One supplier states an MOQ of 10 pieces for mixed standard bearings against 5,000 pieces for bearings customized with your brand, with samples of 1–10 pieces and an average lead time within 15 workdays²⁶.

Those are single-supplier figures, but they show why quantity and branding must be settled before the RFQ is sent rather than after the quote comes back.

• ✓Full designation plus bore, outside diameter and width written out
• ✓Operating temperature, shaft fit, speed, load direction and dust or moisture environment
• ✓Clearance class, precision class and seal suffix stated or requested
• ✓Quantity, unit of measure and whether the demand is one-time or recurring
• ✓Acceptable brand or manufacturer pool, and whether equivalents are permitted
• ✓Documentation list: ISO 9001, MTR, ATEX or RoHS where applicable, inspection certificates for the highest grades
• ✓Required delivery date and whether expedite is needed

When should you accept a modified bearing?

When the standard part cannot meet the application or the delivery date, the modified route is worth asking about. Standard off-the-shelf bearings can be modified with DLR oil holes and O-ring grooves, EDM lubrication holes, inner race reliefs, ID/OD reductions, lubrication grooves, anti-rotation slots, precision spacers and custom preloads⁵.

These modifications turn a catalogue bearing into an application-specific component, and one supplier states they can reduce lead times compared with fully custom designs⁵. That is a supplier claim, not a general rule, so treat it as a question to put to each supplier rather than a planning assumption.

The trade-off is that a modified bearing changes the price basis: the RFQ now has to describe the modification, not just the catalogue number. For high-speed, high-temperature or safety-critical applications, the sources say to consult the equipment OEM or a bearing specialist rather than rely on cross-reference alone¹⁶.

If your failed bearing is in a spindle and the standard replacement has a long lead time, ask the supplier what modifications they can apply to a stock bearing and what that does to the delivery date.

Where the sources disagree

Two sources stating different figures for the same item means at least one is a marketing or supplier position rather than a measured value. The buyer who anchors on one number negotiates against a figure the other side may not recognise.

The precision-class dispute is the clearest: one source reports ABEC 5 accounts for 49.7% of ABEC-rated bearing market revenue, while the same source warns against defaulting to it because ABEC 1 serves roughly 90% of industrial applications adequately^19,22.

The lead-time dispute matters for planning: one supplier states an average lead time within 15 workdays for both peak and off-peak seasons, while another states that modifying standard bearings can reduce lead times compared with fully custom designs, implying custom routes run longer^5,26. Neither is a market rate.

For your RFQ, ask each supplier for their own committed date against your quantity and modification, and treat any published average as a starting point only.

What the sources do not establish

• No unit-of-measure convention for bearing quantity in an RFQ
• No convention for expressing one-time buy versus recurring annual demand
• No guidance on stating expedite requirements or stock-availability checks
• No rule on whether equivalents or reconditioned bearings are acceptable, or how to signal that
• No bearing-specific RFQ template or field checklist
• No method for specifying runout or tolerance values beyond the class label
• No country-of-origin or traceability field defined for an RFQ