INA Bearings Catalog: 6 Checks to Run Before You Approve a Bearing Spec

I'm a quality engineer at an industrial drive supplier, and I review every bearing specification before it reaches customers—roughly 200 unique specs per year. I've rejected about 12% of first submissions in 2024, and almost none of those rejections were about the bearings themselves. They were about incomplete information: missing load direction, wrong tolerance class, or a dimension misread from the INA bearings catalog.

This is the checklist I run on every order. It takes maybe twenty minutes, and it has saved us from several five-figure redo situations over the last couple of years.

Who This Checklist Is For

If you're replacing a bearing on a machine that's down, designing a bearing arrangement into new equipment, or staring at the INA bearings catalog wondering which of the 40 similar-looking codes is actually the one you need—this is for you. The only requirement is that you can describe what the bearing is supposed to do. The checklist handles the rest.

Step 1: Write Down the Load Conditions Before Opening the Catalog

Most people open the catalog first. They browse the range of bearings, think “that looks right,” and end up ordering whatever matches the part number that's already in the machine.

That approach breaks when the original bearing was slightly wrong to begin with, which happens more than most teams realize. Yes, the machine ran, but it ran hot, or noisily, or with a service life shorter than it should have had. Blind replacement is a gamble.

Write these down first:

• Load direction — radial (perpendicular to the shaft), axial (along the shaft), or a combination?
• Load magnitude — constant, shock, or fluctuating?
• Speed — including start-stop cycles, not just the nameplate RPM.
• Temperature — at the bearing housing, not the room temperature.
• Environment — dust, moisture, coolant splash?

My first quality manager used to say it better than I can:

“The catalog is the answer key, not the starting point.”

Take a few minutes to write down the real load conditions before you flip to the dimension tables. If you can't answer one of the five items above, that's the problem to solve first.

Step 2: Match the Bearing Family to the Load Direction

This is where the classic question usually surfaces: “What's a thrust bearing?” Fair question, so here's the direct answer.

A thrust bearing is a bearing designed primarily to handle axial load—load that pushes along the axis of the shaft. A radial bearing handles load perpendicular to the shaft. Different geometries, different jobs, and one can't simply be swapped for the other.

INA's product lines follow this logic for rotary applications:

• Radial loads: deep groove ball bearings, cylindrical roller bearings, and INA needle roller bearings—a good option when radial mounting space is tight.
• Axial loads: INA thrust bearings. Cylindrical roller thrust bearings for heavy axial loads, axial angular contact ball bearings for higher speeds.
• Combined loads: angular contact ball bearings or tapered roller bearings, usually mounted in pairs.
• Linear motion: INA linear bearings, including linear ball bearings and profiled rail guides. Quick note: linear bearing load ratings don't translate directly from rotary bearings (not that this stops people from trying).

One detail I check on every thrust bearing order is the direction of the load. A single-direction thrust bearing supports load in one direction only. If the load reverses, you need a double-direction thrust bearing, or a pair of single-direction units set up correctly. I rejected an 80-piece order in Q3 2024 because the drawing specified a single-direction thrust bearing where the application clearly had reversing axial load. The redo cost $15,000 and added two weeks to the customer's timeline. So glad we caught it before shipping—we were one line item away from a very awkward phone call. And the correct answer was in the catalog, page two of the thrust bearing section, in bold.

Step 3: Use the Ball Bearing Size Chart as the Final Authority

When it comes to dimensions, the ball bearing size chart in the catalog is what decides things. Not the product photo. Not the 3D model in your CAD library. The table.

One common point of confusion: metric bore codes. For codes 04 through 96, the bore is the code multiplied by 5 mm. So a 6204 has a 20 mm bore, and a 6220 has a 100 mm bore. For codes below 04, there's a special table: 00, 01, 02, and 03 correspond to 10, 12, 15, and 17 mm. If you see “20” in a code and assume “20 mm,” you'll be off by a factor of five. That seems too obvious to be a real problem, until you watch a 6220 being unboxed for a 20 mm shaft. (I have. It's an awkward conversation.)

Also worth checking while you're in the table: the width series. A 6200-series and a 6300-series with the same bore code have different outside diameters and widths. They're close enough to be confused, but they are not substitutes. The size chart catches this in seconds.

Step 4: Don't Skip the Tolerance Class

Most bearing specs I receive contain the bearing number, the quantity, and a delivery date. That's about it. It's like ordering a car by exterior color and leaving the engine unspecified.

INA bearings are available in tolerance classes following ISO 492: normal (often labeled P0), plus P6, P5, and higher. Normal class serves most applications fine. P5 provides tighter geometric precision at a higher price. Specifying P5 for a slow-crawling conveyor is wasted budget. Specifying normal for a high-speed spindle is planning for premature failure.

There's also the internal clearance group (C2, normal, C3, C4), defined per ISO 5753. This one gets skipped even more often. In applications with a tight shaft fit and high operating temperature, the effective internal clearance drops—and C3 may be the right call. A bearing that dies early isn't necessarily a bad bearing. It might be a normal-clearance bearing placed in a C3 application.

If you ask me, tolerance class and clearance group should appear on every BOM line. It prevents more field failures than any other single line item.

Step 5: Verify the Shaft and Housing Fits Before You Order

The bearing doesn't work alone. It sits on a shaft inside a housing, and those two interfaces determine how much of the bearing's rated life you actually get.

The Schaeffler technical catalog, which contains INA's engineering data, includes ISO-based fit recommendations: shaft seats in the js6/k6 range, housing bores in the H7/J7 range, depending on loading. These tables are not there to fill pages. A loose fit lets the inner ring creep and fret on the shaft. An overly tight housing bore distorts the outer ring and changes the bearing's internal geometry.

One drawing error I flag repeatedly: a keyway cut directly under the bearing seat. The keyway interrupts the bearing seat surface, so the inner ring doesn't sit perfectly round on the shaft. The bearing runs slightly out of true and wears unevenly. It's not visible during assembly—it shows up later as uneven heating or vibration. I've rejected more than one shaft drawing for exactly this reason.

Step 6: Check the Components Connected to the Shaft

This is the step that gets skipped most often, in my experience: accounting for what's mounted on the same shaft as the bearing.

Take a conveyor drive running 3/4 pitch roller chain. The chain pull creates a lateral force on the shaft, and that force has to be included in the bearing load calculation. A bearing selected based only on the weight of the shaft and sprocket will look fine on paper and can fail surprisingly early under real load. I've seen it happen on a packaging line, where the initial bearing selection completely omitted the sprocket's chain pull.

Also verify the sprocket bore fits the shaft, and that there's room for the sprocket hub or lock collar next to the bearing. If there isn't, you'll be machining the shaft during installation. That's where total cost explodes—not on the bearing price, but on unplanned machine work and downtime. Whether it's a 3/4 pitch roller chain, a V-belt pulley, or a coupling, the bearing is part of a system. The system defines the bearing's job.

Mistakes That Come Back to Haunt Specs

If you take only one thing from this checklist, let it be this: the most expensive bearing mistake is not buying the wrong part. It's when the wrong part runs long enough to make it into mass production, or onto a machine rebuild, before the problem becomes visible.

Quick list of the errors I flag most:

• Confusing the width series in the size chart. Same bore, different outside diameter. Always verify against the table.
• Ignoring load direction. A thrust bearing is a great solution when it's the right one. It survives exactly zero seconds of being loaded in the wrong direction.
• Buying on unit price instead of total cost. The cheap bearing that fails early costs multiples more once labor, downtime, and replacement logistics are added. The correct bearing with the right tolerance and clearance is the cheaper investment.
• Assuming all INA linear bearings are interchangeable. Linear ball bearings and profiled rail guides serve different precision and load requirements. They're separate product families in the catalog for a reason.

Take this with a grain of salt if you want. But these six checks turn a bearing order from a guess into something you'd put your name on. In my line of work, that's the whole point.