A machined brass cage is cut from a solid ring of brass, with pockets milled or drilled and the halves joined. It is heavier and far more expensive than a stamped steel cage, but it holds its shape at 250 °C, retains a film of lubricant in the pockets, and stays balanced at speeds where a stamped cage would start to rumble.
Brass keeps its strength to 250 °C and does not soften abruptly, which is why it appears in dryer rollers, kiln applications and hot pumps. Polyamide would be a puddle at those temperatures, and a stamped steel cage would still work but distorts under repeated thermal cycling in large sizes.
The second letter describes what the cage is centred on. MA is centred on the balls, MB on the inner ring. An inner-ring-centred cage runs with a controlled clearance on the ring land, which is more stable at very high speed; a ball-centred cage is simpler and cheaper. When replacing an MB with an MA you change the running clearance of the cage, which can show up as noise.
Brass is roughly three times the density of polyamide and the machining is slow. For a small motor, a brass cage would add inertia and price with no benefit. Brass earns its place in large or fast bearings, not in small ones.
| Designations | M (ball-centred), MA (ball-centred), MB (inner-ring centred) |
|---|---|
| Material | Machined brass, sometimes leaded |
| Temperature | Up to 250 °C |
| Speed | Very high — good balance, low distortion |
| Lubricant retention | Excellent — brass holds oil in the pockets |
| Cost | The highest of the common cages |
| Weight | High — adds inertia |
| Typical use | Large roller bearings, hot applications, high-speed machinery |
| Criterion | Brass M | Steel J | Phenolic T |
|---|---|---|---|
| Temperature | 250 °C | 150 °C | 120–150 °C |
| Speed | Very high | High | Highest |
| Balance at speed | Excellent | Good | Excellent |
| Weight | Highest | Low | Low |
| Lubricant retention | Excellent | Moderate | Good |
| Cost | Highest | Lowest | High |
| Typical use | Large roller, hot duty | General | Spindle |
The default — cheap, strong, temperature-safe
Read →PA66 — quiet and cheap, 120 °C limit
Read →Resin-bonded fabric — highest speed
Read →Two stamped halves joined by rivets
Read →One-piece snap-over retainer
Read →One-piece machined — for large roller bearings
Read →M is the designation for a machined brass cage, ball-centred. MA and MB are variants: MA ball-centred, MB inner-ring-centred.
Only if the running temperature stays below about 120 °C and the lubricant is compatible. Above that the polyamide softens and the pockets deform.
It is better than stamped steel at very high speed because it stays balanced and does not distort. Phenolic is better still for the very highest spindle speeds because it is much lighter.
Send the designation, the three dimensions and the quantity — we reply with price, brand options and lead time within 30 minutes on working days.