The letters get swapped on supplier pages, in catalogues and in purchase orders, and almost always in the same direction. Here is what each grade actually controls, what the numbers are, and which upgrade is worth paying for.
By the Juding Engineering technical team · Published 23 October 2026 · 16 min read · Last verified: 2026-10-23
TL;DR
- Z is the vibration class and V is the precision class. Z1 to Z4 control how much vibration a rotating bearing generates, while V1 to V3 control manufacturing precision and rotational accuracy. Most supplier pages invert this.
- Z1 allows 2.8 mm/s r.m.s., Z2 allows 1.8 mm/s, Z3 allows 1.2 mm/s and Z4 allows 0.9 mm/s of velocity vibration measured over the 100 Hz to 1000 Hz band.
- V1 allows 1.2 mm/s, V2 allows 0.9 mm/s and V3 allows 0.6 mm/s, so V1 is numerically identical to Z3 and V2 is numerically identical to Z4.
- That means specifying V1 instead of Z3 buys you tighter dimensional and runout tolerances, but not a quieter bearing. V3 at 0.6 mm/s is the only V class that is actually quieter than any Z class.
- The Z steps are not evenly spaced: Z1 to Z2 is a 35.7 percent reduction, Z2 to Z3 is 33.3 percent and Z3 to Z4 is only 25.0 percent, so each upgrade buys less than the one before it.
- Vibration grade is not noise grade. Acoustic noise in decibels is a separate classification, and the ISO 15242 measuring method has nothing to do with the grease noise test symbols defined in the ISO 21250 series.
- ISO 15242-1:2015 is the measurement standard: it specifies measuring methods for vibration of rotating rolling bearings under established conditions, together with calibration of the measuring systems, and is confirmed current as of 2026.
- On a motor order, the grade matters most where noise reaches a person rather than a microphone: fan motors, ceiling fans, air handling units and appliance motors running near a customer.
Bearing grade letters are routinely reversed on supplier pages, and the reversal almost always goes the same way. Z is the vibration class and V is the precision class: Z1, Z2, Z3 and Z4 limit how much vibration a rotating bearing generates, while V1, V2 and V3 describe bearings built to tighter manufacturing precision and rotational accuracy. Once you have that fixed, the numbers are simple. Z1 permits 2.8 mm/s r.m.s., Z2 permits 1.8 mm/s, Z3 permits 1.2 mm/s and Z4 permits 0.9 mm/s of velocity vibration in the 100 Hz to 1000 Hz band, while V1 permits 1.2 mm/s, V2 permits 0.9 mm/s and V3 permits 0.6 mm/s.
The part that changes how you buy is what happens when you put those two ladders next to each other. V1 at 1.2 mm/s is numerically identical to Z3, and V2 at 0.9 mm/s is numerically identical to Z4. So specifying V1 does not give you a quieter bearing than Z3. It gives you the same vibration ceiling with tighter dimensional and runout tolerances. Only V3 at 0.6 mm/s is actually quieter than any Z class.
Where the Z and V Letters Get Swapped
The most common error in bearing specification is offering V1, V2 and V3 as vibration grades and Z1, Z2 and Z3 as noise grades, which inverts the meaning of both families. It appears often enough that it is worth seeing a real example rather than describing one, because the error is not subtle once you know where to look.
Our own 6203 ceiling fan ball bearing page lists the available options as Vibration V1, V2, V3 and Noise Z1, Z2, Z3. The families it offers are right, because the machine can supply all seven. What is wrong is the heading attached to each one. Written the standard way round it should read Vibration Z1, Z2, Z3 and Precision V1, V2, V3.
This matters commercially rather than pedantically, in three ways. A buyer who believes V is the quieter family will pay for V1 expecting a quiet bearing and receive Z3-level vibration. A supplier who writes the headings this way has probably not read the standard, which is a reasonable signal about how carefully the rest of the specification sheet was written. And in a contract dispute, a grade specified under the wrong heading is a specification you cannot enforce.
The one-line correction. Vibration is Z. Precision is V. If a quotation offers you V1 to V3 as vibration grades, ask them to restate it, because you are being quoted something different from what you think you are buying.
What the Z Vibration Classes Actually Limit
The Z classes limit vibration velocity r.m.s. over the 100 Hz to 1000 Hz band, measured on the outer ring of the rotating bearing under the load, lubrication and speed conditions defined in the measurement standard. It is a mechanical measurement, not an acoustic one, and that distinction is the source of most of the confusion in this area.
The measurement conditions are not negotiable in a useful sense. They are fixed so that a Z2 from one factory and a Z2 from another factory mean the same thing. That is the entire purpose of the grade system, and it is why a bare number without a reference to the measurement standard is not a specification at all.
One more point deserves emphasis for anyone buying sealed bearings. Because the seal or shield is part of the bearing construction and contributes its own contact and drag characteristics, a Z figure quoted for a sealed or shielded version is not directly comparable with the same Z figure quoted for an open bearing. The letters and numbers match, but the thing being measured is not identical. If your motor needs both sealing and a vibration grade, state both in the same line and ask the supplier to confirm which construction the figure applies to.
The Z1 to Z4 Values and the V1 to V3 Values
The two ladders together cover 2.8 mm/s down to 0.6 mm/s, and the V classes overlap the top two Z classes exactly rather than sitting above or below them. The table below puts them side by side, which is the fastest way to see why choosing between the two families matters less than most buyers assume.
| Grade | Family | Velocity r.m.s. limit (mm/s) | Step reduction from previous | What it actually controls |
|---|---|---|---|---|
| Z1 | Vibration | 2.8 | Baseline | Vibration velocity only |
| Z2 | Vibration | 1.8 | 35.7 percent | Vibration velocity only |
| Z3 | Vibration | 1.2 | 33.3 percent | Vibration velocity only |
| Z4 | Vibration | 0.9 | 25.0 percent | Vibration velocity only |
| V1 | Precision | 1.2 | Identical to Z3 | Precision, rotational accuracy and dimensional tolerances, with a Z3-level vibration ceiling |
| V2 | Precision | 0.9 | 25.0 percent | Precision, rotational accuracy and dimensional tolerances, with a Z4-level vibration ceiling |
| V3 | Precision | 0.6 | 33.3 percent | The only class quieter than any Z class |
So the honest way to read this table is that V1 and V2 exist for applications where you need precision control more than you need extra quietness. Choosing V1 over Z3 buys you tighter runout and tighter dimensional tolerances, because that is what the V family is for; it does not buy you a quieter bearing, because both sit at the same 1.2 mm/s ceiling. V3 is the exception and it is genuinely different, sitting 1.5 times below Z4 and 4.67 times below Z1.
Why the Z Steps Are Not Evenly Spaced
Each step up the Z ladder reduces the permitted velocity by a smaller percentage than the step before it, which means the top of the ladder is the most expensive place to buy marginal improvement. Working through the arithmetic makes this easy to see.
From Z1 to Z2 the reduction is 35.7 percent. From Z2 to Z3 it is 33.3 percent. From Z3 to Z4 it is only 25.0 percent. The V ladder behaves differently at the top, because V2 to V3 goes back up to a 33.3 percent reduction. Because Z4 is the smallest single step on the ladder, a buyer who needs a genuine improvement is usually better served moving from Z2 to Z3 than from Z3 to Z4 for the same budget.
That is a procurement observation rather than a technical one, but it follows directly from the numbers and it changes what a sensible specification looks like. In practice most motor applications do not need better than Z2 or Z3, and the applications that genuinely justify a low grade are acoustic rather than mechanical.
Vibration Grade Is Not Noise Grade
Bearing vibration is measured in millimetres per second as velocity, acoustic noise is measured in decibels, and grease noise is a third measurement again with its own symbol set, so the three should never be used interchangeably in a specification. This is the second confusion that follows the first, and it is the reason the supplier pages that get Z and V wrong often also conflate noise with vibration.
The ISO 15242 measuring method has nothing to do with the grease noise series. The ISO 21250 series on rolling bearing grease noise testing uses the symbols BQ+ for regular greases, MQ for greases formulated with low noise additives and NQ for quiet greases, and grades the grease rather than the assembled bearing. Specifying a grease symbol instead of a bearing vibration class changes what is being controlled and what is being delivered.
Where acoustic noise genuinely matters, a vibration grade is still useful but it is not the same thing. A Z2 bearing in a fan motor gives a predictable mechanical noise floor; whether the finished appliance meets a sound pressure requirement in decibels is a separate question that depends on the housing, the impeller, the mounting and the operating speed.
How ISO 15242 Measures the Grade
ISO 15242-1:2015 specifies measuring methods for vibration of rotating rolling bearings under established measuring conditions, together with the calibration of the related measuring systems. That single sentence contains the two things that make the grade system trustworthy: fixed conditions and calibrated instruments.
According to the ISO catalogue, ISO 15242-1:2015 Rolling bearings, Measuring methods for vibration, Part 1: Fundamentals is Edition 2 from December 2015, runs to 16 pages, is maintained by ISO/TC 4/SC 13 under ICS 21.100.20 and was last reviewed and confirmed in 2026. It replaces the withdrawn ISO 15242-1:2004. Its companion ISO 15242-2:2015 covers radial ball bearings with cylindrical bore and outside surface and a contact angle up to and including 45 degrees.
The practical consequence is that a supplier claiming a Z or V grade should be able to tell you which measurement conditions they used and that their equipment is calibrated. If they cannot, the letter and number on the box are a label rather than a specification, and you are entitled to treat them that way.
ISO 15242-1:2015 specifies measuring methods for vibration of rotating rolling bearings under established measuring conditions, together with calibration of the related measuring systems.
ISO 15242-1:2015 abstract, ISO catalogue entry verified 23 October 2026
Other Grade Families on the Same Bearing
A complete bearing specification carries four independent grade families plus a seal suffix, and conflating them is the most common ordering error on multi-line schedules. Keeping them in separate clauses in the specification removes almost all of it.
| Family | Common values | What it controls | When it matters |
|---|---|---|---|
| Z class | Z1, Z2, Z3, Z4 | Vibration velocity r.m.s. over 100 to 1000 Hz | Fans, appliance motors, anything a person hears |
| V class | V1, V2, V3 | Precision, rotational accuracy and dimensional tolerances | Alignment-critical, sealed or high-speed applications |
| P class | P0, P6, P5 | Rotational accuracy and radial runout | Where runout drives a sealing or balance requirement |
| C class | C0, C2, C3 | Internal clearance | Tight fits, thermal growth and expansion joints |
| Suffix | ZZ, 2RS, 2Z, open | Shield or seal type | Dust, moisture, lubricant retention and drag |
A worked example is our 6203 deep groove ball bearing for ceiling fan and motor applications, measuring 17 by 40 by 12 mm with a mass of 0.064 kg and offered in precision classes P0, P6 and P5, clearance classes C0, C2 and C3, and with both the V and Z families available. That is five separate decisions, and a specification that says only 6203 has left all five open.
The lower friction side of the same story is covered on our 6002 ZZ low friction low noise deep groove ball bearing page, where the seal, the grease application and the sealing checks are treated as specification items in their own right rather than as a note at the bottom of the table. That is the right way round: because the seal and the lubricant each change the friction and the noise, they belong on the same line as the grade.
How to Write a Bearing Grade Into a Motor Specification
Seven steps, and the order matters because the first decision determines which letter is even eligible.
- Decide whether you need vibration control or precision control. Vibration control suits applications where the noise reaches a person. Precision control suits applications where runout and dimensional consistency affect alignment, sealing or a critical clearance.
- Use the correct letter. Write Z for a vibration class and V for a precision class. Do not accept a quotation that offers V classes as vibration grades.
- Choose the number against a real application requirement. For an open deep groove ball bearing in a fan motor, Z2 at 1.8 mm/s is a common working specification, Z3 at 1.2 mm/s is where acoustic expectation rises, and Z4 or V3 are for genuinely quiet premium applications.
- State the bearing construction alongside the grade. Say open, ZZ or 2RS in the same line, because a Z figure for a sealed bearing and a Z figure for an open bearing are not the same specification.
- State the measurement standard and the band. Reference ISO 15242 and require the velocity r.m.s. figure over 100 Hz to 1000 Hz. Without the standard and the band, a bare number has no agreed meaning.
- Separate the other grade families into their own clauses. Precision class, internal clearance and seal suffix belong in separate lines of a bearing schedule.
- Require the measured value from the actual batch. A nominal class statement is weaker than a reported measured value per batch, and confirm the quality management standard the supplier holds is current at the time of supply.
The last point is not a formality. Certifications expire and get replaced, and a specification sheet that names a superseded revision tells you nothing about the process running today. Check the revision on the certificate rather than assuming the brand’s reputation carries the detail.
Do You Actually Need a Grade Here?
Most motor bearings do not need a vibration grade at all, and specifying one on an industrial motor nobody can hear is the most common way buyers spend money without getting anything. The grade earns its cost where vibration is transmitted into something a person experiences.
Ceiling fans are the clearest case, which is why a dedicated fan bearing product makes sense. Air handling and ventilation fans are the second, because the fan is usually near the occupied space even when the motor is not. Appliance motors exposed to the customer are the third, particularly washing machines, dishwashers and kitchen extraction, where the motor is inside the product the customer is standing next to.
For an industrial pump motor on a rigid base, in a plant where the nearest person is thirty metres away, the grade is rarely the best place to spend money. In that case the money is better spent on the seal type, the grease specification and the life rating. If you are not sure whether a bearing carries a load, speed or an acoustic requirement that justifies a grade, specify the standard bearing first and upgrade only when a measured problem exists.
Specifying Bearings for an OEM Build?
Send us the bearing designation, the application, the operating speed and the acoustic requirement, and we will tell you which grade family applies, whether your current specification is internally consistent, and what the measured value should be for the batch you receive. If you are ordering in volume, we can hold the batch and report measured values against it rather than against a nominal class.
Review our precision bearing range for bulk orders first, or contact the team through the contact page.
Frequently Asked Questions
What is the difference between bearing grade Z1 and Z2?
Z1 and Z2 are both vibration velocity classes for normal precision bearings. Z1 permits a maximum of 2.8 mm/s r.m.s. and Z2 permits 1.8 mm/s r.m.s., measured over the 100 Hz to 1000 Hz band under the conditions defined in ISO 15242. Z2 is therefore about 36 percent quieter than Z1.
Is V1 quieter than Z2 on a bearing?
No. V1 permits 1.2 mm/s r.m.s. against Z2 at 1.8 mm/s, but the more useful comparison is against the Z classes: V1 is numerically identical to Z3 at 1.2 mm/s and V2 is numerically identical to Z4 at 0.9 mm/s. Specifying V rather than Z gives you tighter dimensional and rotational accuracy tolerances, not a lower velocity figure.
Which V grade is actually the quietest?
V3, at 0.6 mm/s r.m.s. It is the only V class that is quieter than any Z class, sitting 1.5 times below Z4 at 0.9 mm/s and 4.67 times below Z1 at 2.8 mm/s.
What does the Z grade measure exactly?
Z grades limit vibration velocity r.m.s. over the 100 Hz to 1000 Hz band, measured on the outer ring of the rotating bearing under the established load, lubrication and speed conditions defined in ISO 15242. It is a measure of the mechanical vibration the bearing generates while running, not of the sound it produces.
Is bearing vibration grade the same as bearing noise?
No. Vibration grade is a velocity measurement in millimetres per second. Acoustic noise is measured in decibels and is a separate classification, and grease noise is separately tested under the ISO 21250 series using the symbols BQ+ for regular greases, MQ for greases with low noise additives and NQ for quiet greases.
Which ISO standard covers bearing vibration measurement?
ISO 15242-1:2015 Rolling bearings, Measuring methods for vibration, Part 1: Fundamentals specifies measuring methods for vibration of rotating rolling bearings under established measuring conditions together with calibration of the related measuring systems. ISO 15242-2:2015 covers radial ball bearings with cylindrical bore and outside surface and a contact angle up to 45 degrees.
Can I order a Z grade on a sealed or shielded bearing?
A grade can be specified, but the seal is part of the bearing construction and contributes its own contact and drag characteristics to the measured level. This means a Z figure quoted for a sealed or shielded version is not directly comparable with the same Z figure quoted for an open bearing, and you should ask the supplier to state which construction the figure applies to.
What other grade families appear on the same bearing designation?
Precision classes P0, P6 and P5 control rotational accuracy and radial runout, clearance classes C0, C2 and C3 control internal clearance, and the suffix indicates seal or shield type such as ZZ for metal shields on both sides or 2RS for rubber seals on both sides. These are independent of the Z and V vibration and precision grades.
Do I need a vibration grade for every motor bearing?
No. A grade matters where vibration reaches a person rather than an instrument, which means ceiling fans, air handling and ventilation fans, appliance motors near a customer and any sealed motor marketed on quiet running. For an industrial pump motor on a rigid base where nobody hears it, the grade is rarely the best place to spend money.
What should I ask a bearing supplier to quote?
Ask for the grade stated with the correct letter, the ISO 15242 measurement conditions, the bearing construction the grade applies to, and the measured value from your own specified batch rather than a nominal figure. Also ask which quality management standard is held and whether the certificate is current, because an outdated certification reference tells you nothing about the current process.
Post time: Oct-23-2026