Linear bearings & guides: types, dimensions & brand filters

Round-shaft bushing versus profile rail versus plain guide

In a recirculating rolling guide, elements carry load through a working track, enter an unloaded return path and cycle back into the loaded zone as the carriage moves. A linear plain bearing instead slides its working material along the guide; it has no ball-return circuit.

A drawer slide, sliding door roller and machine-tool rail may all create linear motion, but they are separate assembly types. Their attachment, travel and load specifications cannot be replaced by a bare linear-bearing bore size.

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Closed, adjustable, open, long and flanged bushings

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THK LM and LME designations belong to different dimensional series. Keep the series and suffixes; a matching shaft diameter is not proof of an equivalent outside diameter or mounting length.

THK LM dimensions: shaft diameter is only the first number

This reference table is transcribed from the public THK Linear Bushing Series catalogue, Model LM. Dimensions are nominal shaft diameter dr × outside diameter D × length L, in mm. It is not a universal dimension rule for unbranded 'LM' products or for LME, flanged and housed versions.

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The catalogue's UU designation indicates seals at both ends. The public THK LM8UU record independently confirms 8×15×24 mm. Note the difference between LM 8S at 17 mm long and LM 8 at 24 mm long; neither is automatically a long LM-L version.

These are nominal identification dimensions, not shaft/housing tolerances, clearance values or a current availability statement. Verify the complete current model drawing before replacement. An LM11949 tapered-roller component is not an LM linear bushing merely because its name starts with LM.

Profile-rail size, block type, preload and accuracy

Rail width alone does not define a carriage. Record the brand and series, block width and length, assembly height, hole pattern, rail section and end details. Preload is an internal load condition; accuracy class describes specified geometric accuracy. Neither is simply another name for stiffness or load capacity.

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A block that slides onto a similar-looking rail is not proven interchangeable. Do not mix brand/series components or transfer a preload code without explicit compatibility evidence.

Shaft finish, support and rotation restraint

A rolling linear bushing uses the shaft as part of its working raceway. Shaft hardness, finish, accuracy and straightness therefore matter; an ordinary steel rod is not automatically a suitable rail. Plain linear bearings have their own mating-surface requirements, which may be different.

One ordinary round bushing on one round shaft does not create a general anti-rotation or moment-resistant axis. Guide spacing, multiple supports, profile geometry or a purpose-designed spline must react the required moments. A ball spline specifically addresses torque transmission during axial travel.

1. Establish whether the motion must allow or prevent rotation about the travel axis.
2. Identify shaft span and support layout, including deflection under load.
3. Specify the bearing-compatible shaft surface and dimensional accuracy.
4. Check the complete support arrangement rather than using one bushing's radial rating as a moment rating.

A linear bearing is not automatically suitable for simultaneous shaft rotation. Use a documented rotary-linear design when both motions are required.

Lubrication and mounting checks

Dry-running polymer guides and grease-lubricated rolling guides are different systems. Seals do not remove the need to identify lubrication requirements. A lubricant recommendation for a ball spline also must not be copied indiscriminately to every linear guide.

1. Identify rolling versus plain construction and obtain its lubrication instructions.
2. Clean mounting references and check rail parallelism, shaft alignment and supporting-surface condition.
3. Use the specified fitting and tightening sequence; do not use excessive clamp force to cure an incorrect fit.
4. Confirm that seals and lubricant access work throughout the stroke.
5. Distribute the specified lubricant as instructed, without assuming a universal grease quantity or travel interval.
6. Check motion over the full usable travel before applying operating load.

Noise, binding, play and flaking: investigate the system

These are investigation paths, not diagnoses from one symptom. Isolate an unsafe mechanism and preserve damage and lubrication evidence before cleaning or replacing parts. NSK's linear-guide troubleshooting treats mounting, contamination, loading and lubrication as possible contributors rather than assigning one cause to every noisy guide.

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3D printers, CNC machines and other linear-motion applications

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These are selection questions, not a claim that any listed model fits an Ender, Prusa, CNC conversion or other specific machine. Exact assembly drawings and operating inputs remain necessary.

Metric or inch? Identify the dimensional series first

A shaft diameter is only the first search field. Also measure the outside diameter and overall length of a bare bushing. For a flanged bearing, record the flange and bolt pattern; for a housed block, record the shaft-centre datum and mounting-hole pitches.

The following tables are manufacturer-specific NB Slide Bush reference data, not a universal interchange catalogue. They extend the THK LM identification table above. NB SM, NB KB and NB SW are separate dimensional series; a similar number or a shared shaft diameter does not prove replacement compatibility.

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Data reviewed 2 October 2026 against NB Slide Bush catalogue pages C-6–C-11 and the series tables identified below. Nominal dimensions are identification values, not manufacturing tolerances.

NB SM metric linear-bearing size and load chart

These are standard, closed-type base designations. SM8s is the short 8 mm version: 8×15×17 mm, whereas SM8 is 8×15×24 mm. The s is significant.

C and C0 are basic catalogue load ratings in newtons, not the allowable load of your complete machine. Load direction, shaft hardness, stroke, moments, support and required life still need checking.

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Source: NB Slide Bush, SM standard type, C-16–C-17. Resin-retainer, corrosion-resistant, seal and accuracy options are separate order-code fields. A blank option must not be assumed to mean sealed.

NB KB European-metric linear-bushing size chart

Both SM and KB use millimetres, but several mounting dimensions differ. For example, SM12 is 12×21×30 mm while KB12 is 12×22×32 mm. A 12 mm shaft alone cannot identify which housing is required.

KBS is NB’s corrosion-resistant version of this series. Do not interpret this NB prefix as evidence about an unrelated brand or copy its dimensions to every product marked KB.

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Source: NB Slide Bush, KB Euro Standard, C-80–C-81. Listed values describe closed base types; open and adjustable variants require their own drawing.

NB SW inch linear bearings: 1/4, 3/8, 1/2, 3/4 and 1 inch

All three dimensions in this table are inches. 0.2500 = 1/4, 0.3750 = 3/8, 0.5000 = 1/2, 0.6250 = 5/8, 0.7500 = 3/4 and 1.0000 = 1 inch. Multiply an inch dimension by exactly 25.4 to convert it to millimetres.

A 1/2 inch shaft is 12.7 mm, not 12 mm; a 1 inch shaft is 25.4 mm, not 25 mm. Do not use a nearby metric bushing as a substitute. SWS2 and SWS3 are the small corrosion-resistant entries actually listed by NB; the table does not invent SW2 or SW3.

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Source: NB Slide Bush, SW Inch Standard, C-100–C-101. Dimensions use the printed inch column. Seals are not available on SWS2 and SWS3. These are not Thomson, THK LMB or other-brand interchange approvals.

Same shaft size, different housing: comparison examples

Use these pairs to narrow an identification search, not to approve substitution. Even an identical nominal envelope does not establish equal clearance, load rating, seal drag or service life.

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Comparisons are derived from the two NB series tables above. This section does not assert that every LM/LME-labelled product follows those dimensions.

Round-flange linear bearings: NB SMF dimensions

SMF has an integral round flange. Here dr is shaft diameter, D is the cylindrical body diameter, L includes the flange, Df is flange outside diameter, t is flange thickness and PCD is the bolt-circle diameter. All dimensions are millimetres.

The source drawing uses four mounting holes. PCD alone is insufficient for installation: verify hole diameter, counterbore, bolt head clearance and the pilot fit on the exact current drawing.

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Source: NB Slide Bush, SMF Round Flange Type, C-26–C-27. These are NB codes, not certified substitutes for LMF, LMK or another manufacturer’s flanged bushing.

Square-flange linear bearings: NB SMK dimensions

SMK uses a square flange. K is the side width across the square, not a shaft diameter and not the diagonal. PCD still describes the four-hole bolt circle. D and L describe the body and overall length; t is flange thickness, all in millimetres.

Changing a round flange to a square flange can change edge clearance, access and how the mounting face carries load. A shared shaft diameter is not enough to make the change.

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Source: NB Slide Bush, SMK Square Flange Type, C-28–C-29. Check the drawing’s corner envelope and counterbores in addition to these nominal dimensions.

Linear pillow blocks and housings: NB SMA GUU size chart

These are complete NB housed round-shaft units, not bare bushings or profile-rail carriages. GUU specifies a resin retainer and seals at both ends in this NB series. It does not mean the unit is maintenance-free.

h is the distance from the mounting face to the shaft centre, not the total block height. W is overall width and L overall length; B and C are the transverse and longitudinal mounting-hole pitches. Dimensions are millimetres; S1 is the metric thread callout for four mounting holes.

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Source: NB Slide Bush, SMA Block Type, C-118–C-119. NB specifies h ±0.02 mm and B/C ±0.2 mm on the drawing. SBR/TBR supported blocks, SC units and profile-rail blocks are not declared interchangeable with this table.

Read the full linear-bushing suffix: UU is not ZZ

Suffix meaning belongs to the manufacturer and product family. Do not apply a rotary ball-bearing suffix dictionary automatically to a linear bushing. In the NB SM catalogue, ZZ identifies two double-lip seals; it does not identify the metal shields commonly meant by ZZ on rotary bearings.

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Source: NB Slide Bush C-11, C-16, C-100. Availability is series- and size-specific; the table is not a recipe for combining every suffix with every listed model.

NB shaft hardness, finish and recommended fits

A ball bushing runs directly on its shaft: the shaft surface is a raceway. NB recommends shaft hardness of at least 58 HRC and surface roughness below Ra 0.4 for the catalogue application. A soft or rough rod can reduce performance even when its measured diameter is correct.

The following fit designations are NB’s recommendations for the stated standard series and accuracy grades. Lower-case letters refer to shafts; upper-case letters refer to housings. They are not universal instructions for every brand, rail or dry-running polymer bearing.

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Source: NB Slide Bush C-9, Table C-9. Do not transfer the table to long, wide, open, adjustable or flanged variants without checking their own entries. Do not point-load a standard bushing with a set screw or add uncontrolled preload.

NB ball-bushing lubrication, temperature and load limits

For these rolling ball bushings, NB recommends lithium-soap grease, or turbine oil in the ISO VG 32–68 range when oil lubrication is selected. Replenishment depends on operating conditions; the catalogue does not support a universal hours-or-kilometres interval for every machine. Clean-room lubricant is a separate selection.

Preservative oil is not a complete lubrication plan. Deliver lubricant to the rolling contact through the approved arrangement; confirm compatibility before changing an existing lubricant. Do not drill an assembled bushing to add an oil hole. NB’s oil-hole option needs its specified manufacturing details.

NB uses a 50 km basis in its ball-bushing rating-life equation. Keep that basis when comparing ratings or calculating life; a rotary-bearing calculator in revolutions is not directly applicable. Open-type load capacity also depends on force direction relative to the opening.

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Source: NB Slide Bush C-7–C-11. These are catalogue component limits, not a prediction of accuracy, grease life or suitability at the limit. Do not apply rolling-bushing lubricant advice to a self-lubricating plain bearing.

THK LM/LME legacy numbers: the 2026 changes are size-specific

THK’s current discontinued-product list records a January 2026 transition for the families and sizes below. This is a same-manufacturer replacement direction, not evidence that all LM or LME products were discontinued, and not a cross-brand interchange approval.

Keep the original marking when identifying an installed bearing. Check the replacement drawing, suffix, seal, load rating and mounting conditions before approving a change. An older dimensional record remains useful for identification even after a product transition.

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Source: THK North America, Discontinued Products and current LM family page, checked 2 October 2026. The list does not justify relabelling an LM8 or LM12 query as discontinued.

Linear rails and carriage blocks: choose the guide before the drive

A profile-rail guide consists of a shaped rail and a matching carriage. The moving table attaches to the carriage; the guide constrains motion along the rail. A round-shaft ball bushing is a different interface. Neither name identifies a complete powered axis.

Start with the required travel, available assembly height, table footprint and mounting access. Then record the force directions, overturning moments, block spacing and duty cycle. A nominal rail-size number is not a shaft-bore measurement or a payload rating.

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These are documented candidate families for investigation, not approvals for a CNC machine, printer or other named piece of equipment.

THK HSR rail and block size chart: 17 exact model references

All dimensions below are millimetres. M×W×L means assembled height × block width × overall block length, not a rotary bearing d×D×B. W1 is the rail width; F is the rail-hole pitch. B×C is the block mounting-hole pattern, and S×l is the tapped-hole designation and depth.

The source specifies L with UU or SS contamination-protection accessories. Other seal, scraper or lubrication options can increase the length. Keep the complete ordering code when comparing a physical assembly.

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Example: HSR25R has a 23 mm rail width in this table. Do not turn the “25” in the series name into an assumed 25 mm rail measurement. This is a reference table, not a fabrication drawing.

HSR dynamic and static ratings: compare like-for-like, not payload labels

C and C0 below are the manufacturer’s basic dynamic and basic static load ratings in kilonewtons. The mass column is one block’s own mass. None of these columns alone is the permissible weight of a complete moving table.

For an application check, include the moving assembly, external forces, offsets, acceleration, block arrangement and the applicable moment ratings. Keep the manufacturer’s life and load conventions; a rotary-bearing RPM calculator is not a linear-guide life calculation.

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Do not add single-block ratings to claim an axis capacity. Load distribution and combined loads must first be established.

Can the rail and carriage be mixed? HSR versus SHS and other limits

THK explicitly states that an SHS block cannot be fitted to an HSR rail: the rail profiles differ. Changing between those families requires changing the rail and block as a set. Matching the size number or assembled height does not override that restriction.

HSR-R and HSR-LR are different block-length variants. THK describes LR as sharing the R cross-section but having a longer block and greater load rating. That family relationship is not a blanket interchange approval for arbitrary clearance classes, special rails or used components.

1. Record the complete maker, rail and block markings. Keep suffixes and special-order identifiers.
2. Match the exact rail profile, block form, mounting pattern, preload/clearance and accuracy specification.
3. Check seals, lubrication accessories and the resulting overall length against the available travel.
4. Confirm how many rails and blocks the stated set contains. A THK single-rail set is not automatically a two-rail machine assembly.

For the HSR RM models in this reference, M denotes stainless-steel block, rail and balls. This does not certify every accessory material or make an unverified mixed assembly compatible.

Linear-guide preload is separate from accuracy grade

In the THK HSR clearance table, no symbol denotes normal clearance, C1 denotes light preload and C0 denotes medium preload. The values below are the manufacturer’s radial-clearance ranges in micrometres (μm), not machining allowances for a shaft or housing.

HSR accuracy grades use a different code: normal (no symbol), H, P, SP and UP. Running-parallelism limits depend on rail length. Specify clearance/preload and accuracy separately; do not translate HSR C1 into a rotary-bearing clearance rule.

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C0 as a preload suffix is not C0 as a static load-rating symbol. Mounting-surface errors also affect service life; preload is not a remedy for a misaligned base.

Linear roller guides: SRG is not a crossed-roller bearing

The THK SRG family uses circulating rollers in four raceway rows. It is a profile-rail guide, not a round-shaft bushing and not a crossed-roller rotary ring. The distinction matters when a search uses only “linear roller bearing.”

Use the SRG family as a candidate where stiffness is a defined design requirement. Its family description does not establish a load, service interval or replacement for an unspecified machine.

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Do not infer rail/carriage interchangeability with HSR from similar external dimensions. A verified matched system is still required.

LM8UU, LME16UU and LM8LUU: read the whole designation

For the THK round-shaft bushing families below, UU denotes seals at both ends. In LM8LUU, L identifies the long version and UU identifies the seals: it is not another name for the standard LM8UU. The tables show the maker’s base reference and the corresponding UU ordering notation, not live stock or a cross-brand standard.

Dimensions are nominal shaft diameter dr × outside diameter D × axial length L, in millimetres. A listing that calls LM8UU “24 mm wide” is referring to its axial length: the reference is 8×15×24 mm, not a 24 mm shaft bore. A pack quantity such as “x 2” does not change the size of either bushing.

Check the maker and the complete marking first. These references do not establish the dimensions of an SKF- or Misumi-labelled part, an unknown seller’s part or a model with a different suffix. LM11949 and LM67048 are not round-shaft bushings from this table.

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Source scope: THK’s public model-coding and dimensional references, checked 3 October 2026. UU examples were checked in the manufacturer’s model-coding illustrations. The tables are identification references, not CAD or a purchasing/availability service.

THK LM / LM-N: standard closed-type size and rating table

The closed-type references below include the current N-designated sizes. LM8S is the shorter 17 mm version; LM8 is 24 mm long. The standard LM8LUU long version belongs to the separate LM-L table.

C and C0 are the published basic dynamic and static ratings in newtons (N), not kilonewtons and not a complete machine payload. Mass is the source table’s base-model reference in grams; it is not a separately verified sealed-configuration shipping weight.

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Only the closed standard/long configuration is tabulated here. The current manufacturer table is the authority for N/NL references. Historical non-N names retain their original identity; these current values do not retrospectively certify their ratings, tolerances or replacement compatibility.

THK LME / LME-N: European-series dimensions and ratings

LME is not just another spelling of LM. For example, LME16UU is 16×26×36 mm, while LM16UU is 16×28×37 mm. Even when outside diameters coincide, lengths and retention geometry may differ.

C and C0 are the published basic dynamic and static ratings in newtons (N), not kilonewtons and not a complete machine payload. Mass is the source table’s base-model reference in grams; it is not a separately verified sealed-configuration shipping weight.

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Only the closed standard/long configuration is tabulated here. The current manufacturer table is the authority for N/NL references. Historical non-N names retain their original identity; these current values do not retrospectively certify their ratings, tolerances or replacement compatibility.

THK LM-L / LM-NL: long-bushing dimensions and ratings

The long family uses two retainers. LM8LUU is 8×15×45 mm and LM16LUU is 16×28×70 mm. The current table lists LM40NL at 151 mm and LM60NL at 209 mm long; keep these published values rather than rounding them to an assumed legacy size.

C and C0 are the published basic dynamic and static ratings in newtons (N), not kilonewtons and not a complete machine payload. Mass is the source table’s base-model reference in grams; it is not a separately verified sealed-configuration shipping weight.

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Only the closed standard/long configuration is tabulated here. The current manufacturer table is the authority for N/NL references. Historical non-N names retain their original identity; these current values do not retrospectively certify their ratings, tolerances or replacement compatibility.

Same shaft, different bushing: LM versus LME versus LM-L

Compare the full envelope before checking a housing. These examples share a nominal shaft diameter, but the model families do not share a universal outside diameter, length or retaining-ring layout. All values are millimetres.

LM20UU and LME20UU both have a 32 mm outside diameter, yet their lengths are 42 and 45 mm. At 25 mm shaft size the corresponding lengths are 59 and 58 mm. A matching bore and outside diameter therefore cannot establish an interchange.

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Before fitting an LM/LME bushing: seals, temperature and support

The dimensional notes limit the listed resin-retainer LM and LM-L models to 80°C; the LME note applies that resin-retainer restriction through size 60. A metal-retainer option does not remove a seal limit: THK also gives 80°C as the seal heat-resistance limit. This is not a claim that every bushing is suitable for continuous operation at that temperature.

For one supported shaft, THK’s LM/LME notes call for two or more separated bushings to avoid applying a moment to a single unit. Actual spacing, shaft deflection, load direction and alignment still need an application check. Do not add the C ratings to claim a permissible table weight.

Before replacement, record the exact construction, shaft specification, outside diameter, axial length, retention details, seal arrangement and operating conditions. AJ/OP dimensional tolerances in the manufacturer’s table are stated before the nut is divided. This overview is not a machining-tolerance drawing.

Questions to settle before selecting a model