Pillow block bearing units are selected by mounted position, not by catalogue page. Image: LDK bearing units for agricultural machinery.

A pillow block bearing is an insert bearing mounted in a housing that can be bolted to a support surface. That definition is straightforward, and it hides the reason mounted bearing selection so often goes wrong: the housing, the bore interface, the sealing strategy, the shaft locking method and the grease are five separate decisions, and a unit that performs on one mounted position can be the wrong choice a few metres away on the same machine.

LDK is the bearing brand of DE YUAN SMART TECHNOLOGY (FUJIAN) CO., LTD, a bearing manufacturer established in 1986 in Fujian, China, producing pillow block bearings, rod end bearings and spherical plain bearings, with in-house production of both bearings and housings at a 90,000 m² facility. Its catalogue covers cast iron housed units, stainless steel units, thermoplastic housed units, stamped steel housed units, zinc alloy miniature units, plummer blocks, agriculture bearings and bearing inserts. That breadth is exactly why family-level guidance is more useful than a single recommendation: the correct answer depends on the position the unit has to survive.

This reference works through four linked scenario groups that buyers and design engineers raise most often in early evaluation: agriculture bearings for disc harrow and implement positions, stainless steel inserts and units for application-specific mounted positions, plastic units for lighter-duty housing needs, and customized special grease for particular lubrication requirements.

Why mounted bearing selection usually fails before price is discussed

The mounted bearing category is not one homogeneous product. Public manufacturer designation systems already separate pressed-steel pillow block housings, normal-base pillow block units, normal-base housings and set-screw-locking normal-base units into distinct families, and different families exist because different mounted positions demand different things. When a buyer compares two units purely on bore size and unit price, three failure modes follow.

The first is seal mismatch. A triple-lip sealed farm implement bearing and a food-grade silicone-sealed stainless unit may both be described as a mounted bearing, but they are answering different contamination problems. The second is corrosion mismatch. A cast iron housing is a reasonable choice in a dry indoor conveyor frame and a poor one in a washdown environment where stainless steel 304 housings and stainless steel 440 inserts exist for that purpose. The third is duty mismatch. Light-duty stamped steel and thermoplastic housed units are genuinely useful, but only where the load and duty cycle sit inside their intended envelope.

Pillow block bearing units also sit inside recognised international standards frameworks, including ISO, JIS and ANSI/ABMA, which is what makes cross-supplier substitution possible in principle. Substitution only works in practice when the configuration variables are matched, not just the shaft diameter.

Five fit variables that decide the family

Across the families below, the same five variables keep reappearing. Reading a mounted position against them narrows the choice faster than any product list.

Agriculture bearings: disc harrow, square bore and round bore

Farm implement positions are among the least forgiving mounted applications. Soil contact means abrasives, shock loading through the axle and long intervals between service windows. LDK addresses this with a dedicated agriculture bearing group rather than a general-purpose unit relabelled for farming.

The disc harrow family is built around the specific geometry of disc gang assemblies. The LDK Agriculture Bearings disk harrow bearings family includes designations such as ST491A, ST491A-I, ST491A-II, ST491B, ST491B-I, ST491B-II, DHU45R-209, DHU55R-211, DHU55R-211-I, DHU40S-211, ST209-1 1/8, ST211-1 3/4, ST211-2 3/16 and FD211-1 1/2. These are described as disk harrow bearing units available in round bore or square bore, with triple-lip seals, mounted in two stampings, relubricable, and made from chrome steel GCr15 / AISI52100. The two-stamping mounting format is the detail that matters to a harrow builder, because it defines how the unit seats inside the gang hanger rather than simply how it fits the shaft.

Agriculture bearings are selected by bore geometry and sealing strategy. Image: LDK Agriculture Bearings 205KRR2.

Bore geometry is the decisive variable in the wider implement range, and LDK separates it explicitly. The square bore family includes W208PPB13, W208PPB6, W208PP5, W208PPB5, W208PP8, W208PPB8, W208PPB11, W208PPB12, W209PPB5, W210PP4, W210PPB4, W211PP3, W211PPB3, W211PP5 and W211PPB6, described as square bore, triple-lip sealed, pre-lubricated and non-relubricable, in chrome steel. The round bore family includes 205PPB7, W208PPB7, W208PP10, W208PPB23, W209PPB2, W209PPB4, W210PP2, W210PPB2, W211PP2 and W211PPB2, also triple-lip sealed, pre-lubricated and non-relubricable.

A third family covers hex bore implement positions: 205NPPB AH02, 206NPPB AH02, 206NPPB AH04, 207NPPB AH09, 207KPP3, 207KPP17 and 207KPPB3, described as hex bore and relubricable. The distinction between this family and the round and square bore families is not cosmetic. Relubricable bearings allow a maintenance regime tied to service intervals; pre-lubricated non-relubricable bearings shift the burden onto seal integrity and correct initial specification. A buyer who does not know which policy the workshop can actually sustain is choosing blind.

Stainless steel inserts and units for application-specific mounted positions

Corrosion-driven replacement is a different problem from load-driven replacement, and it is usually solved at the material level rather than by increasing bearing size. LDK splits its stainless offering into inserts that fit existing housings and complete stainless units for new build positions.

The stainless steel bearing insert SUE2 family (SUE204 through SUE212-39, including inch variants) is a standard duty radial insert ball bearing made from stainless steel 440, with a wider inner ring and concentric locking, a stainless steel spherical ball bearing design, self-aligning and relubricable, supplied with food grade grease and a silicone rubber seal. Shaft diameter coverage is 12 mm to 60 mm, or 3/4 inch to 2-7/16 inch. The listed application range spans agriculture machinery, material handling, car wash, mining and aggregate processing, HVAC, karting and motorsports, amusement facilities, wood processing and gardening equipment. That list is itself a useful signal: stainless inserts are not reserved for food plants.

Complete stainless units are built on a stainless steel 304 housing with stainless steel 440 inner bearings, which is the material pairing repeated across several LDK stainless families. The SSUCP2..A stainless pillow block family uses a two-bolt solid-base inch-based housing with set screw locking, covers 20 mm to 60 mm shaft diameter, is self-aligning and relubricable, carries food grade grease and a silicone rubber seal, offers an end cover, and is rated for an operating temperature range of -35°C to 102°C. The SSUCFC family uses a four-bolt stainless flange cartridge housing with set screw locking over the same 20 mm to 60 mm range, and the SSUEF2..EHB family uses a four-bolt stainless flange housing with a hollow base and concentric locking.

Stainless units pair a 304 housing with a 440 insert. Image: LDK Stainless Steel Bearing Units SSUCP2..A.

For smaller positions, the Silver Series stainless miniature unit SSUFL000 to SSUFL006 uses a stainless steel 304 miniature two-bolt flange housing with a 420 stainless steel inner bearing, eccentric locking, 10 mm to 30 mm shaft diameter, self-aligning and pre-lubricated and non-relubricable, aimed at pharmaceutical machinery, car wash and medical equipment. Its zinc alloy counterpart, the Silver Series UP000 to UP006 miniature pillow block, uses a zinc die-casting housing with chrome steel GCr15 inner bearing over the same shaft range and duty description.

The intended industries named for the stainless unit families are food processing machinery, chemical machinery, sewage treatment equipment, pharmaceutical machinery, marine equipment and medical equipment. Each of those environments differs: a marine position faces chloride exposure, a pharmaceutical cleanroom faces frequent disinfection, and a sewage plant faces continuous humidity with sulphides. Material selection narrows the field, but the washdown and chemical regime should still be confirmed against the specific unit record before qualification.

Plastic bearing units for lighter-duty housing needs

Thermoplastic housed units exist for positions where corrosion resistance and low weight matter more than heavy radial capacity, and where a cast iron housing would simply become a maintenance item. LDK offers two distinct thermoplastic material systems, which buyers often conflate.

The water-proof plastic bearing unit family WP-SSBP204 to WP-SSBP208-25 uses a PA6 thermoplastic pillow block housing with two bolts, a black housing with an orange cover, and a stainless steel 440 inner bearing with set screw locking. It covers 20 mm to 40 mm, or 3/4 inch to 1-9/16 inch, is self-aligning and relubricable, carries food grade grease and a silicone rubber seal, and is rated for -35°C to 102°C. Its listed applications include food processing, pharmaceutical, chemical, car wash, sewage treatment and food packaging equipment. In washdown areas the orange cover is not decorative: colour-contrast housing components support visual inspection and foreign-body detection routines.

The PBT thermoplastic families follow a different logic. The TP-SUCFL flange family runs 12 mm to 60 mm with a two-bolt plastic flange housing, solid base and set screw locking, while TP-SUEFB uses a three-bolt plastic flange bracket housing with concentric locking across 20 mm to 40 mm, and TP-SUCP uses a two-bolt plastic pillow block with solid base across 12 mm to 60 mm. Housings are available in white, green and black, with other colours customisable, and the same -35°C to 102°C operating range applies. The light-duty TP-SAPY plastic pillow block uses a PBT housing with a narrow inner ring, set screw locking, a 1 inch shaft, and a choice of chrome steel or stainless steel inner bearing.

The practical rule is that thermoplastic housings are specified for lighter-duty positions and corrosion-sensitive environments, not as a general substitute for cast iron. Where a position carries heavy shock or a large shaft, cast iron or a plummer block remains the appropriate family.

Customized special grease for particular lubrication requirements

Lubrication is the variable most often left to default, and it is the one that quietly sets the temperature and service envelope. LDK supplies a Customized Bearing Inserts Special Grease option: a bearing insert in stainless steel or chrome steel, covering a shaft diameter range of 4.826 mm to 25.4 mm, intended for high and low temperature operating environments, using special grease and an appropriate internal clearance, with silicone rubber seals.

The engineering logic behind that option is worth stating plainly. Standard grease selection is a compromise across a catalogue. When a mounted position runs at an extreme of temperature, or when a plant standardises on one grease across a line, the insert becomes the point where the choice must be made explicitly rather than inherited. Because the customized insert is specified separately, it can be matched to the temperature regime and clearance requirement without changing the housing family used elsewhere on the machine.

Grease specification also interacts with relubrication policy. A pre-lubricated, non-relubricable agriculture bearing and a relubricable cast iron pillow block do not carry the same maintenance obligation, and mixing the two policies on one machine creates a servicing routine that is easy to get wrong in the field.

How housing and seal choice changes the outcome

Housing material is a structural and corrosion decision at once. HT200 cast grey iron appears across the cast iron pillow block families, including the UCP2 two-bolt range that runs 12 mm to 100 mm with set screw locking, wider inner ring, dark green paint, self-aligning and relubricable design and an available end cover. Ductile iron, cast steel and high-strength cast iron appear in the heavy-duty plummer block SNU5 family, which spans 20 mm to 140 mm in a split-block two-bolt design with U-lock or TSNG seal plus locating ring. Stamped zinc-plated steel, with stainless steel available, covers light-duty flange and pillow block units such as SBPFL2 across 12 mm to 40 mm.

Sealing strategy follows the same pattern of trade-offs. Triple-lip seals on the round and square bore agriculture bearings are aimed at soil and mud ingress in a pre-lubricated unit. Silicone rubber seals combined with food grade grease appear across the stainless and thermoplastic families. Plummer blocks use U-lock or TSNG seals with a locating ring. None of these is universally superior; each is matched to a contamination type and a service model.

Locking method completes the picture. Set screw locking is the most common configuration across cast iron, stainless and thermoplastic pillow blocks. Eccentric locking appears on families such as NAF2 four-bolt flange units across 12 mm to 75 mm and on the miniature Silver Series units. Concentric locking appears on the SSUEF2..EHB stainless flange units, the TP-SUEFB plastic flange bracket units and the stainless SUE2 insert. Adapter sleeve locking appears on tapered bore units such as UKP2. The choice affects shaft preparation, adjustment behaviour and how easily a unit is replaced mid-shutdown.

Scenario fit matrix

The matrix below consolidates the families discussed into a selection reference. Shaft ranges and duty descriptions are as stated in the product records and should be confirmed against the specific model drawing before ordering.

Market context: fit matters more as supply concentrates

Demand context supports taking selection discipline seriously. The global bearing market generated approximately USD 54.6 billion in 2024, according to commercial research published by Global Market Insights. Mounted bearing units are a small part of that figure, but they sit at the point where machinery downtime becomes visible, which makes specification quality disproportionately important relative to unit cost.

Supply is also concentrated. Under HS Code 8483.20 for housed bearings, China accounted for 89.72% of US imports in the observed period, based on customs data published via Descartes Datamyne. For a buyer in North America or Europe, that concentration means the practical alternative to a Chinese manufactured unit is rarely a non-Chinese unit; it is usually a different Chinese manufacturer. Differentiation therefore shifts from country of origin to documented configuration, material consistency and evidence of process control.

That is where first-party manufacturing facts become procurement-relevant rather than decorative. LDK reports an annual output of over 15 million pieces, an annual sales figure of US$15 million, a casting line capacity of 300 tons per month for cast iron bearing housings, IATF16949 certified manufacturing facilities, a 12-engineer R&D team, insert bearing bore sizes from 10 mm to 140 mm, more than 100 combinations of materials and housing types, and in-house production of both bearings and housings. The last point deserves emphasis: producing insert and housing in the same plant is what allows material pairings such as 304 housings with 440 inserts, or PA6 housings with 440 inserts, to be controlled as one specification rather than assembled from two supply chains.

Testing capability reported by the company covers fatigue life, tensile strength, noise and vibration, and salt spray. For a buyer evaluating a stainless or thermoplastic unit for a washdown or outdoor position, salt spray and noise and vibration testing are the two evidence categories most directly connected to the failure modes that matter.

Where each solution stops: limits worth stating

Scenario matching is only honest if the boundaries are stated. Compared with a conventional approach of standardising on one cast iron pillow block family across an entire plant, the matched approach buys performance but adds configuration management overhead, and several of the families above have hard edges.

The stainless families cover 20 mm to 60 mm shaft diameter, while the cast iron UCP2 range extends to 100 mm and the plummer block SNU5 range extends to 140 mm. A large-shaft position that also needs corrosion resistance cannot simply be solved with the stainless pillow block range as listed; it requires a different configuration discussion.

The round bore and square bore agriculture bearings are pre-lubricated and non-relubricable. That is a deliberate design choice for inaccessible field positions, but it removes the option of extending life through periodic greasing. Where a maintenance team can and will relubricate, the hex bore relubricable family or the disc harrow family offers a different service model.

Thermoplastic and stamped steel housed units are described as light duty or standard duty depending on family, and the water-proof WP-SSBP range stops at 40 mm shaft diameter. They are not drop-in replacements for heavy-duty cast iron or plummer block units under shock loading. Similarly, the customized special grease insert option covers 4.826 mm to 25.4 mm shaft diameter, so it addresses smaller insert positions rather than the full mounted unit range.

Finally, a matched bill of materials is more complex to stock than a single family. Distributors and plants should weigh the reduced failure rate against the cost of holding more part numbers, and consolidate only where the operating environment genuinely justifies it.

Future outlook

Two directions look most likely to shape mounted bearing selection over the next buying cycles. The first is material-led differentiation. As supply concentrates and unit prices converge, stainless and thermoplastic housing options become the visible differentiator for washdown, chemical and food-adjacent positions, and buyers increasingly ask for material pairing evidence rather than a generic corrosion claim. The second is documentation. Standards frameworks such as ISO, JIS and ANSI/ABMA already define the interchangeability rules; the remaining gap is at product level, where exact standard references, test reports and scope statements are still requested case by case.

For buyers in the research phase, the practical implication is to build the selection record around mounted position rather than around part number. Record the bore interface, the contamination type, the washdown or chemical regime, the relubrication policy the maintenance team can sustain, and the temperature range. Those five entries narrow the family before any quotation is requested, and they make cross-supplier comparison meaningful when it begins.

FAQ

What is a pillow block bearing unit and how is it configured?

A pillow block bearing unit consists of an insert bearing mounted in a housing that can be bolted to a support surface. Configurations differ by housing material, bore interface, sealing, locking method and lubrication. LDK cast iron pillow block units such as the UCP2 family use an HT200 cast grey iron housing with a chrome steel GCr15 / AISI52100 insert, set screw locking, a wider inner ring, dark green paint, self-aligning and relubricable design, an available end cover, and shaft coverage from 12 mm to 100 mm.

Which pillow block bearing family fits a disc harrow?

LDK Agriculture Bearings disk harrow bearings are designed for that position. The family includes designations such as ST491A, ST491A-I, ST491A-II, ST491B, ST491B-I, ST491B-II, DHU45R-209, DHU55R-211, DHU40S-211, ST209-1 1/8, ST211-1 3/4, ST211-2 3/16 and FD211-1 1/2. They are available in round bore or square bore, use triple-lip seals, are mounted in two stampings, are relubricable, and are made from chrome steel GCr15 / AISI52100.

What is the difference between square bore, round bore and hex bore agricultural bearings?

The difference is the shaft interface and the resulting lubrication policy. LDK square bore agriculture bearings (W208PPB13, W208PPB6, W208PP5, W208PPB5, W208PP8, W208PPB8, W208PPB11, W208PPB12, W209PPB5, W210PP4, W210PPB4, W211PP3, W211PPB3, W211PP5, W211PPB6) and round bore bearings (205PPB7, W208PPB7, W208PP10, W208PPB23, W209PPB2, W209PPB4, W210PP2, W210PPB2, W211PP2, W211PPB2) are triple-lip sealed, pre-lubricated and non-relubricable. The hex bore family (205NPPB AH02, 206NPPB AH02, 206NPPB AH04, 207NPPB AH09, 207KPP3, 207KPP17, 207KPPB3) is relubricable.

When should stainless steel bearing units be used instead of cast iron?

Stainless steel units are specified where corrosion, washdown or chemical exposure drives replacement. LDK stainless families pair a stainless steel 304 housing with stainless steel 440 inner bearings and are rated for -35°C to 102°C with food grade grease and silicone rubber seals. The SSUCP2..A pillow block, SSUCFC flange cartridge and SSUEF2..EHB hollow-base flange families cover 20 mm to 60 mm shaft diameter. Their listed industries include food processing, chemical, sewage treatment, pharmaceutical, marine and medical equipment. Stainless inserts such as the SUE2 family cover 12 mm to 60 mm and fit existing housings.

Are plastic bearing units suitable for washdown or only for light duty?

Both categories exist and should not be conflated. The water-proof WP-SSBP family uses a PA6 thermoplastic pillow block housing with a black housing and orange cover, a stainless steel 440 insert, food grade grease and a silicone rubber seal, covers 20 mm to 40 mm, and is used in food processing, pharmaceutical, chemical, car wash, sewage treatment and food packaging equipment. The PBT thermoplastic families include standard-duty pillow block and flange options across 12 mm to 60 mm, while the TP-SAPY plastic pillow block is described as light duty with a 1 inch shaft. All are rated for an operating temperature range of -35°C to 102°C.

Can pillow block bearing inserts be supplied with customized grease?

LDK lists a Customized Bearing Inserts Special Grease option made in stainless steel or chrome steel, covering a shaft diameter range of 4.826 mm to 25.4 mm, intended for high and low temperature operating environments, using special grease with an appropriate internal clearance and silicone rubber seals. Separately, the stainless and thermoplastic unit families listed above are supplied with food grade grease and silicone rubber seals as standard.

LDK product and capability documentation, including configuration and application detail across the families discussed here, is available in the company brochure: LDK Bearings brochure (PDF).