Angular contact angles A, B, C

An angular contact ball bearing looks like a deep groove bearing but works differently: the balls contact the raceways along a line that is tilted to the axis, so the bearing can carry a heavy thrust load in one direction as well as radial load. The size of that tilt — the contact angle — is set by a suffix, and it changes the bearing's character enough that two same-size bearings with different angles are not interchangeable.

What the angle does

A larger contact angle points the load path more along the axis, so it raises axial load capacity and axial stiffness — but it lowers radial capacity and the limiting speed. A smaller angle does the opposite. The common suffixes:

So a 7206 B and a 7206 C share 30 × 62 × 16 mm but behave differently under axial load. Substituting one for the other quietly changes the thrust capacity, the deflection and the bearing life, even though the size is identical. Match the angle.

One direction only — so they come in pairs

A single-row angular contact bearing carries thrust in one direction only. Load it the other way and the balls try to climb out of the raceway — it fails. Because most shafts see thrust both ways (or need to be held firmly), single-row angular contact bearings are normally mounted in pairs, arranged so that between them they take thrust in both directions and can be preloaded to remove play:

• Back-to-back (DB) — the load lines diverge outward. Wide effective spread, so it resists tilting (moment loads) well. The usual choice for locating a shaft rigidly.
• Face-to-face (DF) — the load lines converge. Less moment stiffness, but more tolerant of misalignment.
• Tandem (DT) — both face the same way, sharing a thrust load in one direction. Used where the thrust is heavy and one-directional.

The arrangement is part of the design of the machine, not something to decide at the bench. Replacing a back-to-back pair with a face-to-face pair changes the stiffness and how the shaft is held.

Universal matching

You cannot take any two single bearings and expect them to make a good pair — put two ordinary bearings back-to-back and the preload is uncontrolled. Bearings intended to be paired freely carry a universal matching suffix (codes such as CB, CC, GA, GB, G) that guarantees a controlled amount of preload or clearance when any two are mounted together. If you are building or replacing a set, match the universal-matching designation as well as the angle — mixing a universal bearing with a standard one gives an unknown preload.

Why a 7206 is not a 6206

A deep groove 6206 and an angular contact 7206 are both 30 × 62 × 16 mm. The deep groove takes light thrust in either direction and can stand alone; the angular contact takes heavy thrust in one direction, must be oriented correctly, and normally needs a partner and a preload. They are dimensionally interchangeable and functionally very different. If a machine was designed around a preloaded angular contact pair, a single deep groove bearing of the same size will not hold the shaft the way it needs to be held.

Replacing an angular contact bearing correctly

• Match the contact angle (A / B / C / AC).
• Keep the same arrangement (DB / DF / DT) and orientation.
• Match the universal-matching and preload class.
• Match the design (E) suffix, cage and precision.

General reference only. Contact angle, preload and arrangement are design decisions — confirm them with the equipment or bearing manufacturer before substituting.