81218-TN bearing: complete specifications & equivalents
The 81218-TN is a ISO 104 radial bearing sized 90 x 135 x 35 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 90 mm |
| Outer diameter D | 135 mm |
| Width B | 35 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | polymer (PA66 glass-fibre reinforced) |
| Basic dynamic load rating C | 232 kN |
| Basic static load rating C0 | 865 kN |
| Fatigue load limit Pu | 90 kN |
| Reference speed (thermal) | 1000 rpm |
| Limiting speed (mechanical) | 2000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1750 g |
| Manufacturer designation | 81218 TN |
| 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 | 3.543 in |
|---|---|
| Outer diameter D | 5.315 in |
| Width B | 1.378 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 22.5 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) | 13 of 28 |
| Bore above smallest 81200-series size | 60 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 81218-TN model number is decoded
Where a thrust ball bearing of the same envelope is exhausted, 81218 TN replaces the ball complement with cylindrical rollers: 90 mm bore, 135 mm OD, rated 865 kN static for steady hook and screw loads. The designation 81218 TN states 812 series, 90 mm bore, glass fibre reinforced PA66 TN cage; shaft and housing washers are also orderable separately as WS and GS parts of the same size. The three components are separable and interchangeable within the size: WS shaft washer, K-cage roller set, GS housing washer, all running on flat, square seats; the glass fibre reinforced PA66 TN cage is standard for this size. One direction only: 81218 TN cannot be reversed to take opposite thrust — mirror a second bearing for reversing shafts, and keep housing and shaft seats square within the ISO 104 tolerances. 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 0.06) is present without clamping the rollers.
Typical equipment & failure modes
Common applications
- slewing and turntable pivots with predominantly axial force
- 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
Known failure patterns
- cage wear from rollers being dragged through unloaded zones under fluctuating thrust
- shaft-washer creep and fretting corrosion on a soft or undersized shaft shoulder
- abrasive paste forming as dust bypasses the housing seals into the open washer set
- brinelling of washer raceways from impact or mounting force applied through the rolling elements
- roller skidding and raceway glazing once the thrust falls below the catalogue minimum axial load (factor A)
Selection pitfalls — read before you substitute
- At 90 mm bore the minimum load (A 0.06) is still small, but a vertical shaft at rest loses it entirely — specify springs or check the rotor weight exceeds F_am at zero speed.
- the 1,000 r/min reference speed is the thermal criterion under load, the 2,000 r/min limiting speed is mechanical and oil lubrication typically raises the usable figure.
- The 232/865 kN ratings assume flat, full-support washer seats; a housing face narrower than the 135 mm washer OD invalidates the rating through edge stress.
- Do not substitute a thrust ball bearing of the same ISO envelope by rating alone: the cylindrical rollers of 81218 TN need different minimum load and lubrication despite the shared 90×135 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 81218 TN size.
- The 232/865 kN ratings and 1750 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
Why does 81218 TN need a minimum axial load?
Below factor A 0.06 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.
Can the 81218 TN take reversing thrust?
No. It carries axial load in one direction only; reversing force unloads and impacts the roller set. Use a mirrored pair of bearings for reversing shafts, with a separate arrangement for radial load.
How should a 81218 TN 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 0.06 minimum load is present.
What are the dimensions and ratings of the 81218 TN?
A 81218 TN measures 90 mm bore × 135 mm outside diameter × 35 mm width (3.543 × 5.315 × 1.378 in). From SKF catalogue PUB BU/P1 17000: dynamic C 232 kN, static C0 865 kN, fatigue limit Pu 90 kN, reference speed 1,000 r/min, limiting speed 2,000 r/min, mass about 1750 g. Raceway diameters Ea 95 mm / Eb 129 mm and minimum load factor A 0.06 guide the seat design.
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.