Angular contact ball bearings: types, dimensions & brand filters

Back-to-back, face-to-face and tandem: what changes?

Duplex means a two-bearing arrangement, not simply two identical boxes. DB and DF oppose the contact directions; DT points them the same way. The required set markings and preload remain part of the specification.

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Direction here means axial force along the shaft, not clockwise or anticlockwise rotation. Read the manufacturer's arrangement drawing rather than orienting bearings from a seal colour or a familiar logo.

Contact angle, axial load and speed

Contact angle is the inclination of the load path relative to the radial plane. Radial loading of a single-row angular-contact bearing generates an axial component, which the complete arrangement must react. A larger angle generally favours axial capacity; a smaller angle is commonly chosen for higher-speed duty.

There is no one angle for every bearing with the same base number. Read the actual brand's angle code, accuracy, cage and preload. A code that means one angle in one catalogue is not a universal cross-brand translation.

What is a Type A bearing? Kaydon Reali-Slim identification

In Kaydon Reali-Slim terminology, Type A identifies an angular-contact thin-section ball bearing. The standard design has a 30° contact angle. Here A is a construction label, not an accuracy grade or a universal suffix for every manufacturer.

Its axial support is directional. Reversing thrust needs an opposing bearing or arrangement; a single Type A should not be treated as bidirectional just because it can rotate either way. Kaydon describes matched back-to-back, face-to-face and tandem sets. An unidentified pair of separate bearings is not evidence of a matched set.

1. Keep the manufacturer, complete designation and set markings together when identifying the bearing.
2. Check axial direction and the opposing support before comparing arrangements.
3. Verify the exact model dimensions, ratings and specified preload. This type definition does not supply those model-dependent values.

Technical basis: Kaydon, Type A angular contact bearings; reviewed 2 October 2026. BearingScope provides identification guidance, not a mounting approval.

Kaydon Reali-Slim Type A vs C vs X

These are contact configurations within the Kaydon Reali-Slim family, not three universal bearing quality levels. Choose the load path before comparing dimensions.

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Kaydon warns against using two Type X bearings on a common shaft because excessive friction torque can result. Do not substitute X for an A pair solely because the envelope fits.

Technical basis: Kaydon, Bearing load scenarios. Numeric capacities, speed limits, dimensional interchange and CAD are not established by this comparison.

Matched pair, double row and four-point contact are different products

A matched pair contains separate bearings with specified pairing properties. A double-row design integrates two ball rows into one bearing. A four-point-contact design is a different single-row construction capable of bidirectional axial support; the NSK design described in its reference uses a split inner ring.

The following NSK reference example demonstrates why equal bore and outside diameter do not establish a replacement. It is a catalogue illustration, not an approval to exchange these assemblies.

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Source: NSK Bearing ABCs, Angular Contact Ball Bearings, 5206/7206ADB comparison. Preserve the assembly designation: the pair's width is not the width of one loose bearing.

What does angular contact bearing preload do?

Preload establishes an internal loading state before the external working load is applied. It can improve shaft positioning and stiffness. Excessive preload raises internal load, friction and heat; insufficient preload can lose the intended stiffness or allow unloading.

Position preload uses the controlled geometry of the bearing set, spacers or adjustment. Constant-pressure preload uses a spring arrangement to maintain an approximately controlled force as positions change. They solve different design problems; tightening a locknut by feel does not select a preload.

1. Record the full set marking, pairing arrangement and specified preload class or force.
2. Identify whether the drawing specifies position preload or a spring arrangement.
3. Retain the specified spacer, shoulder and clamping details; do not exchange one bearing of an unidentified matched set.
4. Check the installed condition using the equipment's stated method. A catalogue base number supplies neither an assembly torque nor an acceptance temperature.

Installation direction and a practical pre-assembly checklist

For a single-row design, mounting force in the wrong axial direction can damage the bearing. The assembly sequence for a DB arrangement can differ from DF. Use the exact arrangement instructions; the following is a preparation checklist, not a universal spindle-assembly procedure.

1. Isolate the equipment and support the shaft. Record the old arrangement before separating parts.
2. Confirm complete bearing/set designations, orientation marks, matched components and the machine drawing.
3. Inspect the shaft, housing, shoulders and spacers against the required dimensions and finish.
4. Select a mounting tool that acts on the ring being fitted. Do not transmit an interference-fit force through the balls.
5. Follow the documented DB/DF sequence and preload method. Do not use the opposite sequence simply because the parts fit.
6. Apply the specified lubricant and inspect the completed assembly before the prescribed controlled run-in.

Unknown preload, fits, spacer dimensions or machine-specific torque remain unresolved inputs. They must not be guessed from d×D×B.

Angular contact versus deep groove or tapered roller

Neither bearing family is automatically better. Write down radial force, axial force in each direction, speed, required stiffness, available space and thermal conditions before comparing candidates. A spindle, pump and bicycle headset do not share one universal selection rule.

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Use the model table without losing the critical suffix

Search the exact marking first. In the model records below, check d, D and width together with the complete product description. A row count or an angle that is absent from a record remains unknown; do not infer it merely from a similar series.

Pumps and compressors can require combined-load support; machine-tool spindles also make stiffness, accuracy and preload important. Those are application starting points, not recommendations for an unspecified machine. For miniature, thin-section, stainless or sealed designs, the exact series documentation is still necessary.

1. Identify single row, double row, four-point contact or a separate matched set.
2. Record load directions and the selected arrangement, including the opposing support.
3. Compare full dimensions and documented angle, precision, cage, material, seal and lubricant.
4. Retain unknown fields and verify the machine limits before treating a candidate as interchangeable.

NSK angular contact numbers and suffixes: read the construction first

A complete number tells you more than the bore. The following rules are specific to NSK Rolling Bearings for Industrial Machinery, E1103d (2025), Part C. Other manufacturers may use different angle, cage or closure codes.

For example, 7000AW combines the 7000A table reference (30° contact angle) with the standard W pressed-steel cage. Adding DB identifies the back-to-back matched arrangement. Its nominal width is two individual widths, not the width of one 7000AW. An unqualified stem still does not establish an optional clearance, preload or grease suffix.

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Source scope: C072–C077 for identification and construction; C086–C113 for the loaded rows. Numerical preload, temperature and machine fitment remain model/application-specific.

Single-row angular contact size chart: exact NSK examples

Dimensions below are d×D×B for one bearing. These are a cross-section of verified catalogue entries, not a complete list of every available angular-contact bearing. Each linked record supplies its own source row, shoulder dimensions, cage, limiting speeds and restrictions.

The 7201BEAT85 and 7301BEAT85 table references are marked high accuracy: dimensional tolerances Class 6 and running accuracy Class 5. That mixed specification must not be simplified to a general P5 or ABEC claim. Complete SU matching and clearance/preload requirements still need confirmation.

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C086–C105: values apply to the printed standard cage. Cr and C0r are radial rating references, not a permissible machine load. A limiting speed is not a guaranteed continuous-duty speed.

One bearing versus a matched pair: 7000AW worked catalogue comparison

All four references below use a 10 mm bore and 26 mm outside diameter. The matched set has 16 mm nominal total width (2×8 mm). The single-bearing and matched-pair load ratings are separate printed columns; dynamic capacity is not found by simply doubling the single rating.

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The catalogue gives load-centre spacing a0 = 18.4 mm for DB and 2.4 mm for DF in this row. These are geometric references, not maximum moment loads. The source mass of 0.019 kg is for one bearing; it has not been presented as a measured pair mass.

Source: C086–C087. Verify actual set markings and the required preload/clearance before assembly. DB and DF also use different shoulder and fillet references.

Double-row angular contact size chart: open, ZZ and DDU

A double-row bearing places both rows in one integrated bearing. It can support axial load in either direction and moment loading within its verified application limits. The table below keeps each printed open, shielded and contact-sealed marking separate.

Notice 5210 versus 5210ADDU: both have the same boundary dimensions, but their radial ratings differ. Equal dimensions are not proof of equal performance. A/B/A1 letters in these double-row markings must not be decoded using the single-row 30°/40° angle rule.

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Source: C106–C109. Oil speeds from open rows are not assigned to closed versions. The source does not establish a grease fill code, temperature rating or numerical contact angle for each of these table stems.

QJ four-point contact examples: axial ratings kept separate

The QJ construction in this NSK catalogue has a two-piece inner ring, a nominal 35° contact angle and a machined-brass cage. The table prints base QJ references; a cage/clearance-qualified supplied marking must still be checked.

Ca and C0a below are axial dynamic and static ratings. They are deliberately not combined with the Cr/C0r radial columns in the preceding charts. For the pure-axial case the catalogue uses Pa = Fa and P0a = Fa. That does not establish a combined radial/axial calculation.

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Source: C110–C113. Do not turn QJ dimensions into an interchange approval for a single-row or double-row angular-contact bearing.

Angular contact equivalent-load calculation: choose angle and arrangement

First solve the actual radial and axial reactions for the complete support arrangement, including the axial force induced by radial loading. Then use the factors for the matching bearing construction. Fr and Fa must use the same units; the ratio branches below assume Fr > 0.

For radial equivalent dynamic load, P = XFr + YFa. Choose the lower-ratio branch when Fa/Fr ≤ e, and the higher-ratio branch when Fa/Fr > e. The following table is specific to the NSK catalogue construction; it is not a universal conversion for every angular-contact product.

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Worked arithmetic example, not a bearing recommendation: a 30° DB arrangement has already-resolved loads Fr = 1 kN and Fa = 1 kN. Fa/Fr = 1, which exceeds e = 0.80. Therefore P = 0.63×1 + 1.24×1 = 1.87 kN, and P0 = 1 + 0.66×1 = 1.66 kN. Use the matched-pair rating for that arrangement when performing the subsequent life or static-safety calculation.

For contrast, the same stated Fr and Fa applied to the listed double-row calculation give P = 0.67×1 + 1.41×1 = 2.08 kN and P0 = 1.76 kN. This arithmetic illustrates why the family and arrangement cannot be dropped from the calculation.

When Fr = 0, do not divide by zero or reuse this branch test blindly. Use the applicable pure-axial method and manufacturer limits. The QJ pure-axial equation is shown separately above; its axial rating must not be fed into a radial-rating field.

Sources: equivalent-load tables on C086–C105 and C106–C109. Static safety, fatigue life, minimum load, lubrication, thermal effects and machine limits are separate checks. These examples do not approve a particular load or installation.

Questions to settle before selecting a model