Double Row Deep Groove Ball Bearing 5208 Bore Diameter Spec

01What the Five Characters Actually Say

A bearing designation is built from blocks, not from one number with a single meaning. Read 5208 left to right and each block answers a different question. The middle block only narrows the family, which is where most quoting errors begin.

The same three block logic runs through the whole single row range, so a part like the 6204 bearing reads the same way. Once you can split one designation, you can split all of them.

The Leading 5 Sets the Row Count

A 6 at the front marks a single row deep groove part. A 5 marks two rows of balls running in the same pair of rings. That one digit changes the width, the load path and the price, so it is the first thing to check when someone quotes a number from memory over the phone.

The 52 and 53 groups both carry two rows. The second digit separates a light series from a medium one, and the difference shows up in the outside diameter rather than in the bore.

The 08 Bore Rule

The last two digits multiply by five. 08 becomes 40mm, 06 becomes 30mm, 04 becomes 20mm, 13 becomes 65mm. The rule holds across the 60, 62, 63, 68 and 69 groups, which is why an engineer can read a bore straight off a label without opening a book. Every part in our deep groove ball bearing range follows it.

Two exceptions are worth keeping in your head. Codes 00, 01, 02 and 03 do not multiply, they map to 10mm, 12mm, 15mm and 17mm. And bores under 10mm are written as the bore itself, so a 608 is 8mm and not 40mm.

02The Bore Is the Only Number the Code Gives You

This is where quoting goes wrong. The 40mm bore is trustworthy because it comes from arithmetic. The outside diameter and the width do not, because a series digit only sorts a bearing into a family.

So a line that says 5208 is not a specification. It is a lookup code that opens a catalog page, and the page gives you the envelope. Without the page, the drawing is the only valid source.

03Single Row and Double Row Side by Side

The useful comparison is the double row design against the single row design at the same bore. That is the choice a designer faces when a housing pocket is already cut.

Where the Second Row Earns Its Space

Two rows put more rolling elements under the same shaft, so radial capacity rises without growing the bore. On a short shaft span, where a wider single row part will not fit and a second bearing position is not available, that is often the entire argument for the double row design.

The layout also absorbs a small amount of shaft deflection better than a narrow part, because two rows share the movement instead of one taking all of it.

Where It Costs You

Speed is the first trade. More balls in contact means more heat at the same rotational speed, so a 52 part rarely matches the speed ceiling of the narrow single row bearing it replaces. If the job is a small motor or a high speed spindle, a single row part such as the 6004 bearing at 20mm bore usually fits better.

Width is the second trade. A housing cut for a narrow bearing will not accept a double row part without a change to the shoulder or the end cover, and that change is a machining job rather than a swap.

04What a 5208 Fits On

A 40mm bore double row part turns up where the radial load is steady, the axial load stays modest, and the housing has room. Four patterns cover most of the work we quote.

• Conveyor and roller assemblies where the load is steady and the shaft span is short.

• Pump and fan shafts where one wider bearing can replace two narrow ones and simplify the housing.

• Agricultural and off highway hubs where shock loads arrive from one direction and the housing is generous.

• Gearbox and drive ends where radial load is high but axial load stays small, one step up from a 6305 bearing sized drive end.

Check that the envelope allows the extra width, and that running speed stays inside the catalog limit for your lubricant.

05Suffixes Change the Part More Than the Code Does

Two bearings can both be called 5208 and still not interchange, because the suffix carries the options. When the suffix is missing, the supplier has to guess, and guessing is how wrong parts ship.

A 40mm bore part bound for a wet conveyor and the same bore bound for a dry gearbox are not the same order.

06Six Things to Confirm Before You Order

Run this list against the drawing before the inquiry leaves your desk.

1. Envelope, all three figures. Bore, outside diameter and width, taken from a drawing or a catalog page, never from the code alone.

2. Row count. Confirm the leading digit is 5. A 6208 is a different part with a different width and a different price.

3. Clearance group. C2, CN, C3 or C4 changes the internal fit. State it, do not leave it to the supplier to pick.

4. Sealing. Open, one shield, two shields or two contact seals. Each option changes drag, ingress protection and the speed ceiling.

5. Precision class. ABEC-1, ABEC-3 or ABEC-5. A conveyor does not need the class a spindle needs, and paying for it buys nothing.

6. Lubrication. Grease grade and fill percentage, or oil. This fixes the running temperature and the relubrication interval.

07Why 5208 on Its Own Is Not an Order

Suppliers see bare four digit codes every day, so they fill the gaps with whatever sits on the shelf. That is how a customer ends up with an open bearing where a sealed one was specified, or CN clearance on a shaft that runs hot and needed C3.

A complete line reads like this. 5208, 40mm bore, double row, C3 clearance, two contact seals, ABEC-3, grease filled. Seven fields, one line, no room for interpretation on either side of the transaction.

08Writing the Line on a Purchase Order

A purchase order is read by someone who has never seen your machine. Write for that reader.

1. Start with the full designation including any suffix, exactly as it appears on the drawing or on the old bearing.

2. Add the three dimensions in the order bore x outside diameter x width, with mm after each figure.

3. State clearance and precision as a class, not as a description such as tight or free.

4. State sealing and lubrication so the supplier cannot substitute an open part and call it equivalent.

5. Add the batch or annual quantity because price breaks with volume, and a supplier who sees a quantity of five will quote a different part than one who sees five thousand.

If the drawing and the old bearing disagree, send both. A photo of the old part beside a caliper reading settles more arguments than a paragraph of description. Our guide to reading a bearing code covers the other digit families if you are working from a label rather than a drawing.

09Questions Buyers Ask About 5208

10From a Code to a Quote

A double row deep groove ball bearing 5208 quote is short once the fields are settled. The bore comes from the code, the envelope from the drawing, and the options from the application.