Industrial MRO Reference Library · Technical Reference

Needle Roller Bearings

Needle roller bearings use long, thin rollers to carry high radial load in a small radial space. This sheet covers drawn cups, machined ring bearings, cage assemblies, thrust needle bearings and track rollers, and how their numbers work.

Ref MRO-0008

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A needle roller is much longer than its diameter. Because the rollers are thin, a needle bearing has a small cross section compared with ball or other roller bearings of the same bore. Many needle bearings run directly on a hardened and ground shaft, with no inner ring. That saves more space but makes shaft hardness and finish part of the bearing. Needle bearings are used in gearboxes, pumps, universal joints, power tools, rocker arms and pivot points.

How to identify

Look at the construction. A drawn cup has a thin stamped outer shell, often with open ends or one closed end. A machined ring bearing has a solid outer ring, sometimes with lips, and may come with or without an inner ring. A cage assembly is rollers in a cage with no rings. A thrust needle bearing is a flat disk of rollers that runs against washers or a hardened face. Read the number on the shell or ring.

Common needle bearing types

Type	Construction	Common designation style	Notes
Drawn cup, open ends	Stamped shell, rollers, no inner ring	Metric HK; inch B, BH, J	Pressed into the housing; runs on the shaft
Drawn cup, closed end	Same with one closed end	Metric BK	Seals off a shaft end
Machined ring with inner ring	Solid outer and inner rings	NA series	For shafts that are not hardened
Machined ring without inner ring	Solid outer ring only	RNA series	Shaft is the inner raceway
Cage assembly	Rollers in a cage	K series	Fits between shaft and bore
Thrust needle	Flat roller and cage disk	AXK with AS or LS washers	Carries axial load only
Track roller and cam follower	Thick outer ring, stud or yoke	KR, NATR, NUTR styles	For cam and track running

How the numbers work

On metric drawn cups such as HK, the digits after the letters give the shaft diameter and width in millimeters. On many inch drawn cups, the digits give the shaft diameter and the width in sixteenths of an inch. Exact series rules vary by maker, so confirm in the maker's catalog.

Key points

Bearings without inner rings need the shaft hardness and finish set by the maker. A soft shaft wears quickly.
Drawn cups are pressed in with a proper mounting tool against the stamped end. Hammering on the shell distorts it.
Thrust needle bearings need flat, hardened running faces or washers.
Seals are available on some drawn cups. Check the suffix.

Common mistakes

Using a bearing without an inner ring on a soft, worn shaft.
Pressing a drawn cup in on the wrong end.
Ordering a thrust needle bearing without its washers.
Cross-referencing inch drawn cups to metric by close size.

Governing standards: No single designation standard is listed for this sheet. Use the bearing maker's catalog for designations, mounting and shaft requirements.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

More in Technical Reference

← All Industrial MRO sheets