Flange linear bearings are used when a round-shaft linear motion system needs a bearing that can be mounted directly to a plate, bracket, table, or machine frame. Compared with a standard cylindrical linear bearing that usually needs a separate housing, a flange type linear bearing combines the bearing body and mounting flange into one compact unit.
The most common flange linear bearing model groups are LMF, LMK, and LMH. They are often selected by flange shape first: LMF for round flange, LMK for square flange, and LMH for oval or cut-flange mounting. However, the correct choice should not be based on shape alone. Shaft diameter, shaft accuracy, available mounting space, load direction, bearing length, seal type, and working environment all need to be confirmed before ordering.
Selection note:
LMF, LMK, and LMH mainly describe the flange mounting shape. They do not replace the need to confirm shaft diameter, shaft tolerance, load condition, lubrication, installation accuracy, and matching linear shaft material. A flange bearing can simplify assembly, but it cannot correct a misaligned or undersized shaft system.
What Is a Flange Linear Bearing?
A flange linear bearing is a linear bushing with an integrated mounting flange. Inside the bearing, steel balls circulate along the bearing raceway while sliding over a hardened linear shaft. The flange allows the bearing to be fixed with bolts, so the bearing can be mounted directly to a machine plate or moving structure.
This structure is useful when the machine designer wants a simpler mounting method than using a separate bearing housing. It can reduce assembly parts, save space, and make the bearing position easier to locate during installation.
Flange linear bearings are commonly used with round linear shafts in automation equipment, small CNC devices, packaging machines, inspection fixtures, sliding tables, laboratory equipment, and light-to-medium linear motion mechanisms.
LMF, LMK and LMH Model Differences
The easiest way to understand flange linear bearing models is to look at the flange shape. The flange shape affects how the bearing is bolted to the mounting plate and how much space the design needs around the shaft centerline.
| Model Group | Flange Shape | Mounting Feature | Typical Use |
|---|---|---|---|
| LMF | Round flange | Symmetrical flange around the bearing body | General mounting plates, compact shafts, balanced layouts |
| LMK | Square flange | Four-corner mounting pattern with clear positioning surfaces | Machine plates, sliding tables, automation brackets |
| LMH | Oval / cut flange | Narrower flange width in one direction | Narrow mounting spaces, side-limited structures, special layouts |
LMF round flange linear bearing for direct mounting around a linear shaft.
LMK square flange linear bearing with a stable four-hole mounting pattern.
LMH oval flange linear bearing for layouts with limited width.
LMF Round Flange Linear Bearing
LMF is a round flange linear bearing. The round flange is arranged around the bearing body and is usually selected when the mounting space around the shaft is relatively balanced. It is a common choice for simple linear shaft assemblies where the bearing needs to be fixed directly to a flat plate.
The round flange shape makes the bearing easy to recognize and install. It is often used in compact automation equipment, small sliding mechanisms, 3D printer-style motion systems, packaging devices, and light-duty fixtures.
When selecting LMF, check whether the round flange diameter has enough clearance from nearby parts. In very narrow structures, a round flange may occupy more side space than expected, and LMH or another compact layout may be easier to install.
LMK Square Flange Linear Bearing
LMK is a square flange linear bearing. The square flange provides a clear four-corner mounting layout, making it convenient for rectangular mounting plates, machine brackets, and sliding tables. It is commonly chosen when the mounting plate has enough width and the designer wants a stable bolt pattern.
LMK is often used in automation systems, light CNC mechanisms, testing equipment, and linear shaft assemblies where the bearing position should be fixed firmly on the plate. The square flange also makes it easier to align the bearing visually with the machine structure during assembly.
When using two LMK bearings on parallel shafts, do not rely on the flange to compensate for poor shaft alignment. The two shafts should be parallel, the mounting surface should be flat, and the bearing centers should match the shaft spacing accurately. Otherwise, the system may become tight, noisy, or uneven during movement.
LMH Oval Flange Linear Bearing
LMH is an oval or cut-flange linear bearing. Its flange is narrower in one direction, so it is useful when the installation space is limited on the side of the bearing. In many machine layouts, LMH is selected not because the motion principle is different, but because the mounting shape fits the available space better.
This type is commonly used in compact automation modules, narrow machine frames, special brackets, and equipment where the designer needs bolt mounting but cannot use a full round or square flange.
When choosing LMH, confirm the flange direction before ordering or machining the plate. The bearing may fit well in one orientation but interfere with nearby parts if rotated. For replacement orders, it is better to send the old bearing model or a drawing with hole spacing and flange direction.
Flange Linear Bearing vs Standard Linear Bearing
A flange linear bearing and a standard cylindrical linear bearing use a similar rolling principle on a round shaft, but the installation method is different. A standard cylindrical type usually needs a separate housing or precision bore. A flange type can be bolted directly to the machine structure.
| Item | Flange Linear Bearing | Standard Linear Bearing |
|---|---|---|
| Mounting method | Bolted directly through the flange | Usually installed inside a housing or machined bore |
| Assembly work | Simpler when the plate layout matches the flange | Needs a suitable housing and bore accuracy |
| Space requirement | Needs flange clearance and bolt space | More compact outside diameter, but requires housing structure |
| Replacement check | Model, shaft diameter, flange shape, bolt hole spacing | Model, shaft diameter, outer diameter, length, housing fit |
Shaft Matching Is More Important Than Flange Shape
A flange bearing can only run smoothly when it is matched with a suitable linear shaft. The shaft should have the correct diameter, surface hardness, surface finish, straightness, and tolerance for the bearing. If the shaft is soft, rough, bent, undersized, or contaminated, the bearing may become noisy or wear quickly even if the flange model is correct.
For DLY linear bearing assemblies, flange linear bearings are commonly matched with hardened linear shafts, chrome-plated shafts, or supported shaft structures depending on the application. The bearing model and shaft model should be checked together rather than ordered separately without confirming compatibility.
Related product pages: Linear Bearing, Linear Shaft, Linear Slider, and Linear Bearing Block and Shaft.
How to Choose Between LMF, LMK and LMH
The flange model should be selected according to the machine layout first, then checked against load, shaft size, bearing length, and environment. The following selection logic is more reliable than choosing only by appearance.
| Selection Question | Preferred Direction | Reason |
|---|---|---|
| Is the mounting space balanced around the shaft? | LMF may be suitable | Round flange layout is simple and symmetrical. |
| Is the mounting plate rectangular with enough width? | LMK may be easier to mount | Square flange matches many plate and bracket designs. |
| Is the installation width limited on one side? | LMH may be considered | Oval or cut-flange shape reduces side clearance requirements. |
| Is there moment load or offset load? | Check long type or use multiple bearings | Flange shape alone does not solve moment load. |
| Is the environment dusty or exposed to chips? | Check sealed type and protection design | Contamination can shorten bearing and shaft life. |
Model Details to Confirm Before Ordering
Flange linear bearing models can look similar across suppliers, but small differences in flange diameter, bolt hole spacing, bearing length, seal type, and shaft fit can affect interchangeability. For replacement orders, confirming the model code alone may not be enough if the old bearing has no clear marking.
| Information | Why It Matters |
|---|---|
| Shaft diameter | The bearing bore must match the linear shaft diameter. |
| Flange type | LMF, LMK, and LMH use different mounting shapes and hole layouts. |
| Bearing length | Standard and long types may have different load and stability behavior. |
| Seal form | Sealed types are often needed in dusty or dirty environments. |
| Flange diameter or width | Confirms whether the bearing fits the mounting space. |
| Bolt hole size and spacing | Important for replacement and plate machining. |
| Shaft material and surface condition | A soft, worn, bent, or rough shaft can damage the bearing quickly. |
When a Flange Linear Bearing May Not Be the Best Choice
Flange linear bearings are practical for many round-shaft motion systems, but they are not the best solution for every application. If the machine requires very high rigidity, high moment load resistance, compact profile-rail accuracy, or heavy cutting stability, a profile linear guideway may be more suitable than a round shaft and flange bearing assembly.
For example, a compact inspection fixture may work well with LMF or LMK bearings on hardened shafts. A machine tool table, high-rigidity gantry, or heavy automation axis may need a square linear guideway or roller guideway instead. The bearing type should match the real load and accuracy requirement, not only the available shaft diameter.
If the application has high moment load, long unsupported shaft span, heavy vibration, or strict positioning accuracy, send the installation drawing before confirming the bearing type. This helps avoid choosing a flange bearing when a guideway or supported rail structure would be more stable.
Summary
LMF, LMK, and LMH flange linear bearings are used to simplify the mounting of round-shaft linear motion systems. LMF uses a round flange, LMK uses a square flange, and LMH uses an oval or cut-flange shape for narrower installation layouts. These model groups help buyers identify the mounting style quickly, but the final selection should also include shaft diameter, bearing length, seal type, mounting accuracy, load direction, and working environment.
For DLY customers, the most reliable way to confirm a flange linear bearing is to match the bearing model with the linear shaft and machine layout together. If the product is used for replacement, provide the old model, shaft diameter, flange shape, hole spacing, and photos. If it is a new design, provide the stroke, load, shaft support method, mounting direction, and environment so the bearing and shaft can be selected as a complete motion unit.
Need help confirming LMF, LMK or LMH flange linear bearings?
Send us the shaft diameter, flange shape, bearing model, bolt hole spacing, installation drawing, and working environment. DLY can help confirm the suitable flange linear bearing type, matching shaft, seal option, and replacement dimensions for your application.
Email: export@dlybearing.com
