1946: INA, Needle Cages and Schaeffler

Most bearing histories are about making a better complete bearing. The history of INA starts the other way round. In 1946 Georg Schaeffler decided to build needle roller cages and rollers as a product in their own right, leaving the customer to supply the raceway. It was a bet on specialisation, and it worked: the company that became part of the Schaeffler group reshaped how machine designers use limited radial space.

This article explains why specialising in the load-carrying element made commercial sense, how a cage-and-roller assembly lets the customer use their own hardened shaft as the inner raceway, how the needle cage reduced section height, how INA grew and later joined FAG and LuK, and why the needle part numbers in catalogues today - HK, BK, K, KZK, NA, NKI and AXK - still look the way they do.

The 1946 decision: cages, not complete bearings

A complete bearing bundles four things: the inner ring, the outer ring, the rolling elements and the cage. Producing all four requires ring forging, raceway grinding, heat treatment and assembly, which means a large factory and a large catalogue. Producing the cage and the rollers alone requires a much narrower set of processes, and it can be sold into other makers' designs rather than competing with them.

Why specialising in the load-carrying element made sense

In the needle roller world the cage and the roller complement are the technically demanding part. The raceways are hardened and ground surfaces that many customers already produce on their own shafts and housings to a suitable hardness and finish. By supplying just the cage and rollers, a manufacturer could offer a high-value precision product without having to make and stock complete bearings in every size.

How a cage-and-roller assembly lets the customer supply the raceway

In a drawn-cup or machined-ring needle bearing the outer ring is part of the product. In a needle cage, it is not. The assembly is a cage holding a full complement of needle rollers, and it is mounted directly on a hardened and ground shaft inside a hardened and ground housing bore. The shaft surface is the inner raceway and the housing bore is the outer raceway.

The shaft becomes the inner raceway

This is the key economy of the design. The material that would have been the inner ring is simply part of the shaft, so the radial section is smaller, the number of parts is lower and the weight falls. The trade is that the customer must control the shaft. Its diameter, hardness and surface finish now determine the bearing's performance as much as the cage does.

Those requirements are specified the same way as any other bearing surface. Where a complete bearing is used the envelope conforms to ISO 15, running accuracy follows ISO 492, and the shaft and housing fits follow the ISO 286 system. A needle cage simply moves more of that responsibility onto the customer's own machining, and the most common mistake is to treat the shaft raceway as an ordinary turned surface. A raceway that is only 0.2 micrometre too rough, or a couple of points HRC too soft, will wear or dent before the cage does.

Needle cages and section height

The needle roller is long and thin relative to a ball or a cylindrical roller of the same diameter, so it distributes load over a line rather than a point, and it achieves a high radial capacity in a very small radial section. A cage of needles can fit into a section height that no ball bearing could, which is what makes it useful in gearboxes, rocker arms, pumps and compact power tools.

The same property is the limitation. Because the rollers are slender, the bearing is sensitive to misalignment and has essentially no axial capacity unless it is combined with a thrust arrangement. A needle cage is chosen for radial load in tight space, not as an all-round replacement for a ball bearing. The principle is worked through in our needle roller guide and the needle roller range.

• Section height matters most. A needle cage fits a radial section that no ball bearing could, which is why it appears in compact gearboxes, rocker arms and power tools.
• Axial load needs a partner. A radial needle cage carries essentially no thrust, so it is often combined with a thrust washer or a separate ball bearing.
• Alignment is critical. Slender rollers tolerate little angular error, so the shaft and housing must be concentric to within a tight tolerance.
• Lubrication must reach the rollers. In a tight section there is little room for grease, so the feed path has to be designed into the housing.

The founding of INA

INA was founded to make these cage-and-roller products, and the specialisation gave it a foothold in markets that wanted a compact radial bearing rather than a complete unit. Over the following decades the range extended from simple cages into drawn-cup bearings, machined-ring needle bearings, combined needle and thrust arrangements, and eventually into a broad industrial and automotive catalogue.

The Schaeffler group structure

In the modern era INA joined with FAG, the historic ball bearing manufacturer, and with LuK, a specialist in clutch and transmission components, to form the Schaeffler group. The combination covers the three technologies a driveline and a machine need: needle and roller bearings for compact radial load, ball bearings for general duty and precision, and clutch and transmission systems.

INA, FAG and LuK

The three names are kept as product brands because each carries a distinct technical identity. For a buyer, the practical consequence is that the same organisation can supply a needle cage for a cramped housing, a ball bearing for a motor and a clutch release bearing for a gearbox, all under one quality system. Our INA and FAG pages list the ranges.

The needle product family and its suffixes

The part numbers look the way they do because they describe two things: the envelope and the construction. The letters tell you whether the assembly is a cage alone, a drawn-cup bearing or a machined ring bearing, and the numbers give the dimensions. Reading them is a matter of knowing the family.

Indicative construction of the common needle families. Letters vary slightly between manufacturers, so confirm the exact construction against the catalogue you are ordering from.

Two conventions are worth knowing. Needle rollers are slender by definition, typically 1.5 mm to 5 mm in diameter and several times that in length, which is what gives the family its load density and its sensitivity to alignment. And the numbers in a drawn-cup designation are often read directly as dimensions: an HK 2020 is a drawn-cup needle bearing with a 20 mm bore and a 20 mm width, so the code is a dimensional statement rather than an arbitrary catalogue index. A needle cage on a 30 mm shaft, by contrast, may occupy a radial section only a few millimetres deep.

Which suffix to use when

The choice follows the surfaces available. If the shaft and bore are already hard enough, a plain cage is the most compact option. If an outer raceway is needed, a drawn cup or a machined ring adds one. If the shaft cannot be hardened, add a separate inner ring. Thrust duty needs the axial family, which is dimensioned completely differently.

Load path and stiffness

Because the needle cage runs directly on the shaft, the stiffness of the assembly is partly the stiffness of the shaft itself. A well-supported, hard shaft gives a stiff, high-capacity bearing; a slender or soft shaft gives a flexible one. The bearing cannot compensate for a poor shaft, so the design has to be considered as a system.

Hardness and roughness limits

When there is no inner ring, the raceway that the needles run on is the shaft surface, and the needle rollers need that surface to be within a specified hardness and roughness band. If it is too soft, the raceway dents and fails; if it is too rough, the rollers wear it quickly. Those limits are the reason the system works and the reason it fails when the shaft is taken for granted.

Typical shaft raceway requirements for a needle cage without an inner ring. Confirm the exact values against the bearing manufacturer's data for the specific series.

A Needle Number Is an Envelope, Not a Raceway

The original decision to sell a cage rather than a bearing still defines the buying rule: a needle part number tells you the envelope and the cage, not the raceway. Use a step-by-step check before you order, and give the shaft the same attention you give the bearing.

1. Read the family letter first to establish whether the part is a bare cage, a drawn cup, a machined ring or an axial assembly.
2. Confirm the envelope from the numbers, then check the radial section height against the space you actually have.
3. Decide whether an inner ring is needed by checking whether the shaft can be hardened and ground.
4. Specify the shaft raceway for hardness, roughness, tolerance and roundness if no inner ring is used.
5. Check the alignment and the axial location, because a needle cage offers little angular tolerance and no thrust capacity on its own.
6. Cross-reference on construction, not on letters alone, using the interchange lookup.

For the wider context, the cylindrical roller range is the heavier-duty neighbour of the needle family, the cage design guide explains the cage material choices behind the letters, and the fits and tolerances guide covers the shaft requirements in detail. The IKO needle bearing story traces the parallel development of the same product family, and the brand directory lists the wider market.