The 25 mm bore of the 51400 Series Thrust Ball Bearings is the 51405: 25 mm bore, 60 mm outside diameter, 24 mm assembled height. This page gives the dimensional row from the table, the shaft and housing fits that suit it, the internal clearance to expect and the mounting, lubrication and failure notes that go with the type.
25 mm Bore Dimensional Row (ISO 104 / DIN 711 / GB/T 301)
| Designation | Bore d (mm) | Outer diameter D (mm) | Height H (mm) | Chamfer r min (mm) |
|---|---|---|---|---|
| 51405 | 25 | 60 | 24 | 1 |
What a 51400 Series Thrust Ball Bearings Does
A thrust bearing is a pair of washers with a rolling element cage between them: a shaft washer, a housing washer and the balls or rollers. It carries axial load only, in one direction for the single direction types and in both for the double direction types, and it must be located radially by something else.
Axial load only. This bearing has no radial capacity whatever — the washers would simply slide across one another — so the shaft must be located radially by a separate bearing. The single direction types take thrust one way and need a minimum axial load at all times to keep the rolling elements rolling instead of skidding.
Speed at 25 mm Bore
No limiting speed is tabulated for this product. Where speed matters, the figure to work to is the one the bearing supplier states for the exact design, cage and lubricant supplied — not a family value.
Shaft & Housing Fit for a 25 mm Seat
With the inner ring rotating under a load whose direction is fixed, the inner ring sees a circumferential load and must be an interference fit, or it will creep on the shaft and fret it. The outer ring sees a point load and takes a transition or clearance fit so that it can shift slowly and spread the wear — and so that one of the two bearings on the shaft is free to take up axial expansion.
| Shaft, light load (P ≤ 0.06 C) | j6 |
|---|---|
| Shaft, normal load (P = 0.06–0.12 C) | k5 or k6 |
| Housing — Axial displacement of the outer ring required | H7 |
| Housing — Normal load, outer ring may still shift | J7 |
| Housing — Normal to heavy load, quiet running, outer ring not displaceable | K7 |
ISO 286-2 tolerance grades, applied per the conventional bearing seat recommendations of ISO 1132-2 and DIN 5425-1, for a SOLID STEEL shaft in a cast iron or steel housing. A hollow shaft, a thin-walled housing or a light alloy housing needs a tighter fit than these, because the seat itself deflects.
Abutment Shoulder & Fillet Radius for 25 mm
The chamfer dimension r min for this size is 1 mm. That figure is a limit on YOUR machining, not just on the bearing: the fillet radius in the corner of the shaft or the housing must be smaller than the bearing's corner radius, or the ring seats on the fillet instead of on the shoulder face and is loaded on its corner.
| Chamfer dimension r min (from the table) | 1 mm |
|---|---|
| Maximum fillet radius on the shaft or housing | 1 mm |
| Shaft shoulder must exceed | 27 mm diameter |
| Housing shoulder bore must be under | 58 mm diameter |
The two shoulder figures are the geometric floor and ceiling: a shoulder outside them fouls the corner radius instead of bearing on the ring face. The practical values sit inside them — the shoulder must contact the ring face over a useful area without touching the seal, the cage or the opposite ring, and it must still leave room for a puller when the bearing is dismounted. Take the working da and Da from the abutment table for the bearing; the ring shoulder height they are built on is not a boundary dimension and is not in this table.
Mounting a 25 mm Bore 51400 Series Thrust Ball Bearings
The ring that carries the rotating load takes an interference fit; the ring under a stationary point load takes a transition or clearance fit so that it can creep slowly and spread the wear, and so that one ring is free to take up axial expansion. With a rotating shaft under a fixed load direction, that means an interference fit on the shaft and a looser fit in the housing. Press only against the ring being fitted — force driven through the rolling elements leaves brinell marks in the raceway before the bearing has run a revolution.
At a 25 mm bore the interference is small enough that a cold press or a light hydraulic press is normally enough; heating the bearing in an induction heater or an oil bath to 80–100 °C above the shaft is the alternative, and never above 120 °C for a standard-stabilized bearing. Keep the heated bearing pressed against the shoulder while it cools, because it shrinks axially as well as radially.
This bearing is separable, which makes mounting easier and mis-mounting easier too: fit each ring to its own seat separately, and do not let the two halves be swapped between bearings once they have run — the raceways wear as a matched pair.
Where a 25 mm Bore 51400 Series Thrust Ball Bearings Is Used
At a 25 mm bore, 51400 series thrust ball bearings are typically found in electric motors, pumps, gearbox layshafts, machine tool auxiliaries, agricultural machinery and general industrial drives — the volume range of the whole bearing industry.
Failure Modes and What They Look Like
- Subsurface fatigue (spalling) — a flake of raceway lifts out and the bearing gets noisy and rough. This is the failure the L10 life calculation predicts — if it arrives near the calculated life the bearing did its job, and if it arrives early the load, the fit or the lubrication was not what the calculation assumed.
- Inadequate lubrication — a polished, then discoloured, then torn raceway, running hot with a darkened grease. It is the most common cause of early failure by a wide margin, and the interval, not the grease, is usually what was wrong.
- Contamination — dents in the raceway with raised edges, then premature spalling from those dents. Wear particles, casting sand and washdown water all do it; sealing and filtration are what prevent it.
- False brinelling and fretting — evenly spaced dull marks at ball or roller pitch, produced by vibration while the shaft is stationary — a machine that travels on a truck, or a standby pump beside a running one. It is not caused by overload and cannot be cured by fitting a bigger bearing.
- Skidding under light load — smeared, matte patches on the raceway. A ball or thrust bearing that is not loaded enough to make its rolling elements roll lets them slide instead, and the film breaks down where they scuff.
Where NOT to Use a 51400 Series Thrust Ball Bearings
- Do not ask a thrust bearing to carry radial load. It has none: the washers slide sideways, and the shaft must be located radially by another bearing.
- Do not run one below its minimum axial load. Thrust bearings need a continuous axial load to keep their rolling elements rolling; run light and at speed, they skid and smear.
- Do not mount the washers on a soft or uneven face. The washer faces transmit the whole load into the housing and the shoulder — a face that is not square and supported over its full width bends the washer and cracks it.
Stepping Up or Down from 25 mm
Within the same series, the next bore up in this series is 30 mm. Changing bore changes the shaft, so it is the last thing to change: when the calculated life at 25 mm is short, the first move is to a heavier diameter series at the SAME bore — the 6300 envelope instead of the 6200, for instance — which raises the rating without touching the shaft. The second is to change type: a roller bearing carries far more radial load than a ball bearing of the same envelope.
