How to Read a Linear Guide Part Number

Oct 6

A linear guide part number is a coded specification. Depending on the manufacturer, it can identify the guide family, nominal rail size, carriage shape, carriage length, preload or radial-clearance class, seal package, accuracy class, rail length, number of blocks, material or surface treatment, and other options.

The most important rule is:

Do not decode a linear guide part number using another manufacturer's naming system.

A THK, Schaeffler, SBC, WON, HIWIN, Bosch Rexroth, NSK, IKO, or other guide number may use:

the same letters for different meanings,
different letters for the same feature,
completely different ordering structures.

Even within one manufacturer, the code structure can change between product families.

For replacement work, the complete part number should therefore be treated as one of the most valuable pieces of information available.

Key Takeaways

A linear guide part number is more than a model name.
The first characters usually identify the guide family or series.
A number such as 15, 20, 25, 30, 35, 45, or 55 commonly identifies nominal size, but not necessarily a literal physical dimension.
Subsequent letters may identify carriage shape, flange style, block length, seals, preload, accuracy, or special options.
Rail part numbers may also encode rail length and mounting-hole details.
Manufacturer codes are not standardized.
The same suffix can mean different things between brands.
Accuracy and preload are separate specifications.
Carriage style and carriage length are separate specifications.
A physically similar replacement may still be wrong if preload, accuracy, rail profile, mounting geometry, or internal raceway design differs.
Never discard punctuation, spaces, hyphens, suffixes, or trailing characters when recording a part number.
When the complete number is unreadable, measurements and photographs can help reconstruct the specification.
Nominal size alone does not establish interchangeability.

Why Linear Guide Part Numbers Matter

Consider two carriages that both appear to be:

size 25 profile rail blocks.

One might be:

flanged,
standard length,
normal preload.

Another might be:

narrow,
long,
higher preload.

A third may have:

special seals,
higher accuracy,
corrosion-resistant treatment.

All three can share the same nominal size.

The complete model number distinguishes those configurations.

That is why a replacement request that says only:

“I need a size 25 bearing block”

is usually incomplete.

What Information Can a Part Number Contain?

Depending on the manufacturer, the complete ordering code can contain some combination of:

manufacturer,
guide family,
nominal size,
carriage type,
carriage length,
flange or narrow style,
quantity of blocks,
contamination protection,
preload or radial clearance,
accuracy class,
material,
surface treatment,
rail length,
rail-hole arrangement,
lubrication option,
special operating condition,
matched-set designation.

Not every guide includes every field.

The General Pattern

A useful conceptual structure is:

FAMILY + SIZE + BLOCK TYPE + OPTIONS + PRELOAD + RAIL LENGTH + ACCURACY + SPECIAL FEATURES

But this is only a framework.

It is not a universal syntax.

Start With the Manufacturer

Before decoding anything, identify the manufacturer.

Look for:

logo,
engraved brand name,
laser marking,
label,
packaging,
machine documentation.

This dramatically narrows the possibilities.

For example:

HSR25C

means something within THK's system.

A similarly structured code from another manufacturer could mean something entirely different.

Step 1: Identify the Product Family

The first letters commonly identify the guide family.

For THK, examples include:

HSR,
SHS,
SSR,
SR,
SRG,
SRN,
HRW.

Each family has its own characteristics.

For example, THK's HSR family is a global-standard full-ball profile rail guide with four-way equal-load capability.

THK separately identifies roller families such as:

SRG,
SRN,
SRW,
HRX.

So the family code can immediately tell you much more than nominal size alone.

Step 2: Identify Nominal Size

After the family code, a number commonly identifies nominal size.

Examples include:

For example:

HSR25

means an HSR-family guide in nominal size 25.

But:

25 does not necessarily mean every critical dimension equals 25 mm.

Rail width, carriage width, block length, and assembled height must still come from the dimensional table.

Step 3: Identify the Carriage Type

Letters following the size often identify the carriage configuration.

This may describe:

flange vs. narrow block,
standard vs. long block,
short block,
mounting direction,
special block geometry.

THK's HSR family, for example, currently includes types such as:

HSR-C,
HSR-LC,
HSR-R,
HSR-LR,
HSR-CA,
HSR-CB,
HSR-HA,
HSR-HB.

The differences are significant.

An HSR-C and HSR-LC can share the same rail family and nominal size while using different carriage lengths and ratings.

Standard vs. Long Can Be Hidden in the Code

A very common distinction is:

standard block vs. long block.

Using THK HSR as an example:

C = flange-type standard-length family,
LC = longer flange-type block,
R = narrow standard block,
LR = longer narrow block.

The exact naming depends on the manufacturer.

Do not assume “L” always means long across every brand.

Step 4: Look for the Number of Blocks

Some ordering codes describe an entire rail-and-block assembly rather than a single carriage.

THK provides a useful example.

Its current model-number documentation gives a sample format resembling:

SHS25 LC 2 ...

where the 2 identifies the number of LM blocks used on that rail.

That number is not the rail size.

It is part of the assembly specification.

Why This Matters When Ordering

THK specifically warns that the number of items constituting one “set” depends on the guide type.

For example, its current ordering documentation shows combinations such as:

SHS25C2SSC1+640L

as a rail-and-block assembly.

If you remove or misread one character, you may change:

quantity,
preload,
sealing,
rail length.

Step 5: Identify Seal and Contamination-Protection Codes

Linear guide part numbers may contain codes for:

end seals,
double seals,
side seals,
metal scrapers,
lubrication devices.

THK's model-number structure, for example, includes a dedicated contamination protection accessory symbol.

This matters in:

machine tools,
woodworking,
grinding,
food processing,
dusty manufacturing environments.

A replacement block with inadequate sealing may fit physically while providing much poorer life.

Step 6: Identify Preload or Radial Clearance

Preload is one of the most important suffixes to preserve.

THK's current ordering example includes:

as a radial-clearance/preload symbol.

For the applicable THK families, its model-number guide identifies:

no symbol = Normal,
C1 = Light Preload,
C0 = Medium Preload.

This is THK-specific.

Do not assume:

C0 means medium preload on every linear guide brand.

Why Preload Code Matters

Changing preload can change:

rigidity,
running resistance,
deflection,
service-life calculation.

A carriage with the correct dimensions but wrong preload may not behave like the original.

This is especially important for:

machine tools,
precision automation,
multi-block tables,
reversing loads.

Step 7: Identify Accuracy Class

Accuracy codes may also appear toward the end of the ordering number.

THK's current nomenclature uses accuracy symbols including:

no symbol = Normal,
H = High,
P = Precision,
SP = Super Precision,
UP = Ultra Precision,

where those classes are available for the guide family.

Again, these are not universal.

A letter P in another manufacturer's code might mean something else entirely.

Accuracy Is Not Preload

This distinction is worth repeating.

Preload code describes internal clearance/loading.

Accuracy code describes geometric manufacturing tolerance.

Do not substitute one for the other when matching a replacement.

Step 8: Look for Rail Length

For rail-and-block assemblies, rail length is often encoded explicitly.

THK commonly uses a structure such as:

+1240L

to indicate:

1,240 mm rail length.

Its official current model-number example labels +1240L as the LM rail length in millimeters.

This is especially useful when reading old machine documentation.

Rail Length Is Not Enough

Even when you know rail length, you may still need:

mounting-hole pitch,
end-hole spacing,
hole type,
G1/G2 dimensions,
joined-rail configuration.

Linear Automation USA's Linear Rail Cut Calculator is designed around these practical cut-length and mounting-hole relationships.

Step 9: Identify Material or Surface Treatment

Some model numbers specify:

stainless steel,
corrosion-resistant treatment,
black coating,
special surface treatment.

THK's current HSR documentation notes that an M symbol in certain HSR model designations identifies stainless-steel components.

Do not generalize that code to another manufacturer.

Step 10: Identify Special Operating Features

Additional symbols can specify configurations for:

high temperature,
vacuum,
cleanroom,
lubrication systems,
joined rails.

For example, THK has specialized families such as:

HSR-M1

for high-temperature applications.

Special-environment suffixes should never be discarded during replacement identification.

A Complete THK Example

THK's published model-number coding gives a particularly useful example:

SHS25 LC 2 QZ KKHH C0 F S +1240L P Z T F S -Ⅱ

THK breaks this down into fields including:

Code PortionTHK MeaningSHS25Model / nominal sizeLCLM block type2Number of blocks on same railQZQZ LubricatorKKHHContamination-protection configurationC0Radial-clearance/preload symbolFBlock surface treatmentSSpecial block feature+1240LRail length in mmPAccuracy symboladditional suffixesRail treatments/special features/set information

This is one of the clearest examples of why the entire number matters.

What Happens If You Record Only “SHS25”?

You would know:

manufacturer family,
nominal size.

But you could still be missing:

carriage shape,
carriage length,
block quantity,
seals,
lubrication package,
preload,
accuracy,
rail length,
special treatment.

That may not be enough to order a replacement.

A Real SBC Example From Linear Automation USA

Consider the current listing:

SBC SBI 25 SLL K1

Linear Automation USA currently identifies this as:

SBC,
SBI series,
size 25,
slim-line carriage,
48 mm wide,
108 mm long,
40 mm overall height,
standard preload.

The part number is:

SBI 25 SLL K1

Even without treating every character as universally transferable, the number clearly distinguishes this block from many other SBC size-25 products.

Compare It With Other SBC Size-25 Blocks

Linear Automation USA's current SBC catalog includes size-25 designations such as:

SBI 25 CL K1,
SBI 25 CLL K1,
SBI 25 FL K1,
SBI 25 FLL K1,
SBI 25 FLS K1,
SBI 25 HL K1,
SBI 25 HLL K1,
SBI 25 SL K1,
SBI 25 SLL K1.

They all contain:

SBI 25

but they are not the same carriage.

That is a perfect example of why “SBC 25” is not a complete replacement specification.

The Same Family Can Have Multiple Preload Codes

The current Linear Automation USA SBC catalog also lists otherwise similar carriage configurations with:

suffixes.

This illustrates another critical principle:

Do not drop the last two characters because the block dimensions appear correct.

Suffixes often contain performance-critical information.

A Real WON Example

Consider:

WON H 25 F UU G0

Linear Automation USA currently describes this carriage as:

WON H-series,
size 25,
flanged carriage,
70 mm wide,
83 mm long,
36 mm overall height,
normal preload,
full-ball type.

The ordering code contains multiple meaningful fields:

H 25 F UU G0

Again, do not assume the individual WON suffix meanings translate directly to SBC or THK.

WON Shows Why Every Letter Matters

Linear Automation USA currently lists multiple WON H-series size-25 variants, including:

H 25 F UU G0,
H 25 FL UU G0,
H 25 R UU G0,
H 25 RL UU G0,
H 25 SF UU G0,
H 25 SFL UU G0,
H 25 SR UU G0,
H 25 SRL UU G0.

They share:

H 25

but clearly represent different carriage configurations.

Even a Trailing Suffix Can Matter

Linear Automation USA also currently lists:

H 25 F UU G0 2LF

alongside the base:

H 25 F UU G0

designation.

That is exactly why you should record the entire engraved or printed designation rather than stopping once you recognize the family and size.

A Schaeffler Replacement Example

Another current example is:

Schaeffler KWLT15-H-V2-G4

Linear Automation USA identifies this as a Schaeffler linear guide carriage and a corresponding replacement for the applicable Ewellix LLT product when the correct equivalent has been selected.

The complete designation is:

KWLT15-H-V2-G4

A request for only:

“KWLT15”

would omit important suffix information.

Why Hyphens and Spaces Matter

Part numbers are commonly written with:

spaces,
hyphens,
slashes,
plus signs.

Do not “clean up” the number when recording it.

Write exactly what you see.

For example:

KWLT15-H-V2-G4

should not be reduced to:

KWLT15

or rewritten casually as:

KWLT 15 H

unless the manufacturer's documentation specifically uses that format.

Photograph the Marking Before Cleaning the Machine

For MRO and maintenance teams, this is one of the most useful habits.

Before:

removing the carriage,
cleaning it,
discarding packaging,
scraping corrosion,
sending components to scrap,

take clear photographs of every marking.

Photograph:

top of carriage,
both sides,
end caps,
rail marking,
machine assembly,
any label or barcode.

That information can save hours during replacement identification.

Do Rails and Carriages Have Different Part Numbers?

Often, yes.

A manufacturer may have one designation for:

carriage,

and another for:

rail.

A complete assembly code may then combine both.

Do not assume a block number automatically provides:

exact rail length,
rail-hole spacing.

Likewise, a rail marking may not tell you:

preload,
block style.

Carriage Number vs. Assembly Number

This is an important distinction.

You may find:

a carriage-only number

engraved directly on the block.

The original purchase order may contain:

an assembly number

describing:

two blocks,
one rail,
rail length,
accuracy,
preload,
seals.

Both are useful.

Do not assume they should look identical.

What If the Part Number Is Incomplete?

This happens frequently.

You may only be able to read something like:

...25...LL...

Do not guess.

Record the visible characters exactly and then gather dimensions.

Critical Measurements When the Number Is Missing

Measure:

Rail

rail width,
rail height,
rail length,
mounting-hole diameter,
counterbore diameter,
mounting-hole pitch,
first-hole/end distance.

Carriage

overall width,
overall length,
installed height,
mounting-hole spacing,
thread size,
flange or narrow configuration.

Also note:

number of rails,
number of blocks,
mounting orientation.

Installed Height Is Especially Important

Two nominal size-25 systems can have different:

assembled heights.

If the replacement changes guide height, it can shift:

machine table,
screw alignment,
tooling datum.

Part-number identification should therefore be verified against physical dimensions.

What If There Is No Manufacturer Logo?

Use a combination of:

visible characters,
dimensions,
carriage geometry,
mounting-hole pattern,
rail cross section,
machine age,
country of origin if known,
photographs.

A partial model number plus accurate dimensions is much more useful than a guess.

Do Not Identify a Guide From Color Alone

Carriages may be:

black,
gray,
steel,
plated.

End caps may have manufacturer-associated colors.

But color should only be treated as a clue.

It is not enough to establish:

manufacturer,
family,
compatibility.

Do Not Identify From Nominal Size Alone

One of the most common mistakes is:

“The old rail is 25, so any size 25 carriage should work.”

That is unsafe.

Size 25 guides can differ in:

raceway geometry,
rail width,
rail height,
assembled height,
block width,
bolt pattern,
preload,
accuracy.

Do Not Mix Carriages and Rails Without Explicit Compatibility

Profile rail carriages and rails are precision-matched mechanical designs.

Even when:

nominal size matches,
external dimensions look close,

internal raceway geometry may differ.

Use only combinations supported by:

manufacturer documentation,
verified interchange engineering.

What Does “Interchangeable” Mean?

The word can have several meanings.

Rail/Block Interchangeability

One carriage can operate on the existing rail.

Dimensional Interchangeability

The replacement has the same critical mounting envelope.

Functional Interchangeability

It also provides appropriate:

load capacity,
preload,
accuracy,
sealing,
life.

The best replacement requires all relevant forms of compatibility.

Part Numbers Are Especially Important for Legacy Equipment

Older machines may contain products that are:

discontinued,
renamed,
acquired by another manufacturer.

A complete legacy number can help establish a cross-reference.

Linear Automation USA's current Schaeffler/Ewellix replacement listings are a useful example of this type of transition.

Ewellix and Schaeffler Example

Linear Automation USA currently notes that Ewellix is now part of the Schaeffler Group on its Ewellix product pages and provides replacement assistance for legacy Ewellix components. For example, the current Ewellix LBBR 40-2LS listing preserves the legacy Ewellix designation while directing users toward current replacement support.

This is another reason not to discard an obsolete part number.

It may be the best key to finding the modern equivalent.

How to Search a Linear Guide Part Number

Use this sequence.

1. Search the Exact Number in Quotes

Example:

"SBI 25 SLL K1"

2. Search With the Manufacturer

Example:

SBC "SBI 25 SLL K1"

3. Remove Only Suspected Spacing

Try:

SBI25SLLK1

but retain the original recorded version.

4. Search the Family and Size

If the complete number is unavailable:

SBC SBI 25

5. Compare Manufacturer Documentation

Find the:

official catalog,
dimensional drawing,
model-number key.

6. Verify Physical Measurements

Never rely entirely on search results.

A Part-Number Identification Checklist

Before ordering a replacement, confirm:

ItemConfirmed?Manufacturer□Complete part number□Guide family□Nominal size□Carriage style□Standard/long block□Rail width□Installed height□Block width□Block length□Mounting pattern□Preload□Accuracy□Seal package□Rail length□Rail-hole pitch□Special treatment□Replacement compatibility□

For an unknown guide, this checklist is far safer than matching only the printed size.

A Practical Three-Level Identification Method

At Linear Automation USA, a useful way to think about identification is in three levels.

Level 1: Identity

Determine:

manufacturer,
family,
size.

Level 2: Configuration

Determine:

carriage shape,
length,
preload,
accuracy,
seals,
special options.

Level 3: Machine Compatibility

Verify:

installed height,
mounting pattern,
rail profile,
rail-hole geometry,
load ratings,
moments,
life.

Only after all relevant levels are satisfied should a replacement be treated as confirmed.

Common Linear Guide Part-Number Mistakes

Mistake 1: Recording Only the Size

“25” is not enough.

Mistake 2: Dropping the Suffix

The suffix may identify preload, accuracy, seals, or carriage style.

Mistake 3: Assuming Every “L” Means Long

Codes are manufacturer specific.

Mistake 4: Assuming Every “P” Means Precision

Again, manufacturer specific.

Mistake 5: Ignoring Hyphens

Preserve the exact number.

Mistake 6: Confusing Rail and Carriage Numbers

They can be separate components.

Mistake 7: Ordering From a Photo Without Dimensions

Verify geometry.

Mistake 8: Matching Nominal Size Across Brands

Nominal size does not prove compatibility.

Mistake 9: Ignoring Preload

A physically fitting block can still behave differently.

Mistake 10: Ignoring Accuracy Class

This can reduce machine performance.

Mistake 11: Assuming a Cross Reference Is Automatically Drop-In

Verify the exact original configuration.

Mistake 12: Throwing Away the Old Carriage Too Soon

Keep it until the replacement is fully confirmed.

Linear Automation USA's Perspective

At Linear Automation USA, the complete part number is the starting point for identification—not the end of the process.

When someone sends us:

“I need a size 25 carriage,”

we still need to determine:

manufacturer,
family,
block style,
length,
preload,
accuracy,
rail compatibility.

A complete model such as:

SBI 25 SLL K1

is dramatically more useful because it narrows the configuration immediately.

But even then, for critical replacement work, we prefer to confirm the component against:

dimensional data,
rail geometry,
machine requirements.

This becomes especially important with obsolete components.

Legacy systems can involve:

old manufacturer names,
revised part numbering,
corporate acquisitions,
product transitions.

A correct cross-reference should preserve the machine's required function—not simply produce a block that looks similar.

Our preferred replacement workflow is:

complete marking → manufacturer catalog → configuration decode → physical measurements → rail compatibility → machine requirements → verified replacement

We also recommend preserving photographs and dimensional records after the replacement is complete.

That creates an internal MRO record for the next repair.

Linear Automation USA currently supplies and supports profile rail products from Schaeffler, SBC Linear, and WON Linear, including identification and replacement support.

Our rule is:

Never throw away characters in a linear guide part number until you know exactly what they mean.

Frequently Asked Questions

What Do the Numbers in a Linear Guide Part Number Mean?

A number such as 25 commonly indicates nominal guide size, but the meaning must be verified from that manufacturer's nomenclature.

What Do the Letters Mean?

Letters can identify series, carriage type, block length, preload, accuracy, seals, materials, or special options. Their meanings are manufacturer specific.

Does “25” Mean the Rail Is 25 mm Wide?

Not necessarily. Nominal size is not always literal rail width.

Does L Always Mean Long Block?

No. Never interpret an individual letter without the manufacturer's model-number guide.

Is P Always Precision Accuracy?

No. It may mean Precision in a particular manufacturer's system, but codes are not universal.

Is C0 Always a Preload Code?

No. THK uses C0 for a particular preload/radial-clearance condition in applicable families, but another manufacturer may use C0 differently.

Can I Use a Carriage With the Same Size Number?

Not automatically. Rail profile and raceway geometry must match.

Can I Replace a Block Without Replacing the Rail?

Sometimes. The manufacturer must support block/rail interchangeability or the replacement must be verified as compatible.

What If My Part Number Is Unreadable?

Photograph the component and record rail width, rail height, carriage dimensions, installed height, mounting-hole pattern, and visible markings.

Should I Keep the Old Carriage?

Yes, until the replacement is completely verified and installed.

Need Help Identifying a Linear Guide Part Number?

For the fastest identification, provide:

manufacturer name,
every visible character on the carriage,
every visible character on the rail,
clear top photograph,
clear side photograph,
end photograph,
rail width,
rail height,
block width,
block length,
installed height,
rail length,
mounting-hole pitch,
quantity required.

If the component is obsolete, include:

machine manufacturer,
machine model,
approximate machine age.

Contact Linear Automation USA with this information for help identifying or evaluating a linear guide replacement.