81234-M bearing: complete specifications & equivalents
The 81234-M is a ISO 104 radial bearing sized 170 x 240 x 55 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 170 mm |
| Outer diameter D | 240 mm |
| Width B | 55 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 540 kN |
| Basic static load rating C0 | 2280 kN |
| Fatigue load limit Pu | 200 kN |
| Reference speed (thermal) | 560 rpm |
| Limiting speed (mechanical) | 1100 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 9300 g |
| Manufacturer designation | 81234 M |
| Standard | ISO 104 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 11.1 cylindrical roller thrust bearings |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 11.1 cylindrical roller thrust bearings) · extracted 2026-09-27
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 11.1 cylindrical roller thrust bearings); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & 81200-series range
| Bore d | 6.693 in |
|---|---|
| Outer diameter D | 9.449 in |
| Width B | 2.165 in |
| ISO bore code | 34 |
| Radial section height (D−d)/2 | 35 mm |
| Smallest bore in 81200-series | 30 mm |
| Largest outer diameter in 81200-series | 420 mm |
| Width range across 81200-series | 16–95 mm |
| Bore position in 81200-series (smallest first) | 21 of 28 |
| Bore above smallest 81200-series size | 140 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 81234-M model number is decoded
SKF supplies 81234 M as a separable thrust bearing: the 170 mm shaft washer (WS), the machined brass M cage holding short cylindrical rollers, and the 240 mm housing washer (GS) can be ordered and mounted individually. The designation 81234 M states 812 series, 170 mm bore, machined brass M cage; shaft and housing washers are also orderable separately as WS and GS parts of the same size. Small sizes ship with machined brass M cages to guide heavy rollers at the lubricant limit; the 540 kN rating assumes oil or grease reaching the full washer face. Selection arithmetic: C 540 kN against C0 2280 kN gives a C0/C ratio of 4.22 — thrust bearings are chosen on static rating and F_a/C0 more often than on L10 life. Press only on washer backs, never through the roller set; seat both washers against full-area square shoulders, and shim the housing cover so the minimum load (A 0.42) is present without clamping the rollers.
Typical equipment & failure modes
Common applications
- crane hook crossheads carrying pure hook thrust while the hook swivels
- screw jack and lifting screw thrust positions under slow, steady load
- vertical electric motor and pump shafts whose rotor weight loads one bearing
- extruder and injection press screw thrust blocks at low speed
Known failure patterns
- smearing at roller-raceway contacts during unloaded startup before the oil film or preload is established
- washer back-face fretting where the seat is too narrow to support the full ring face
- oil starvation at the sliding contact zones of large spherical roller thrust bearings on forced-feed trips
- electrical erosion of raceways on VFD-driven shafts without grounding or insulation
- cage wear from rollers being dragged through unloaded zones under fluctuating thrust
Selection pitfalls — read before you substitute
- At 170 mm bore the washers are too stiff to conform to a non-square seat: machine the shoulders parallel or the roller ends concentrate load into a narrow stripe across 55 mm.
- Factor A 0.42 is a mounting requirement, not advice: below the minimum axial load the rollers skid at speed — most "mysterious" early thrust failures are unloaded running.
- Keep the machined brass M cage out of chemical contact with aggressive EP additives beyond its compatibility list; cage damage here redistributes rollers and destroys the washer in hours.
- Do not substitute a thrust ball bearing of the same ISO envelope by rating alone: the cylindrical rollers of 81234 M need different minimum load and lubrication despite the shared 170×240 mm outline.
- The separable washers are not interchangeable across series: an 811 and an 812 washer for the same bore differ in OD and height — order WS/GS parts by the full 81234 M size.
- The 540/2280 kN ratings and 9300 g mass are SKF catalogue values transcribed from ch. 11.1 of PUB BU/P1 17000 (PDF table page 892); mounting data — Ea/Eb raceway diameters and the minimum load factor A — appears in the running text because the structured record carries the boundary envelope only.
Frequently asked questions
How should a 81234 M be mounted?
Interference fit for the shaft washer, sliding fit for the housing washer, full-area square shoulders both sides, press on washer backs only, and shim the cover so the rollers turn freely while the factor-A 0.42 minimum load is present.
What are the dimensions and ratings of the 81234 M?
A 81234 M measures 170 mm bore × 240 mm outside diameter × 55 mm width (6.693 × 9.449 × 2.165 in). From SKF catalogue PUB BU/P1 17000: dynamic C 540 kN, static C0 2280 kN, fatigue limit Pu 200 kN, reference speed 560 r/min, limiting speed 1,100 r/min, mass about 9300 g. Raceway diameters Ea 184 mm / Eb 233 mm and minimum load factor A 0.42 guide the seat design.
How is the 81234 M designation read?
The first three digits 812 give the dimension series (heavy 812 series); 34 encodes the 170 mm bore (code 34 × 5); the suffix denotes the machined brass M cage. WS and GS washers of the same size can be ordered separately.
Why does 81234 M need a minimum axial load?
Below factor A 0.42 the cylindrical rollers skid instead of rolling, glazing and smearing the washer tracks. Springs, preload shims or rotor weight must keep the thrust above the catalogue minimum, especially during unloaded starts.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 11.1 cylindrical roller thrust bearings on 2026-09-27. Read our editorial & correction policy.