Pillow Block Bearing Sizes: What You Need to Know Before You Buy
If you need a quick answer: pillow block bearing sizes are defined by the bore diameter of the inner ring, typically ranging from 12 mm (0.47 in) to 100 mm (3.94 in) for standard units, with shaft sizes from 1/2 inch to 3 inches covering the majority of industrial applications. The housing dimensions, bolt hole spacing, and overall footprint vary by manufacturer but generally follow ISO and AFBMA standards for interchangeability.
Choosing the wrong size bearing is one of the most common and expensive mistakes in mechanical assembly. A bearing that is too small for the load will fail prematurely; one that is too large wastes money and may not fit the mounting surface. This guide covers every dimension you need — bore diameter, housing dimensions, load ratings, and material specifications — so you can select the right pillow block bearing with confidence.
12–100 mm bore range (standard)
½–3" inch shaft coverage
ISO/AFBMA interoperability standards
How Pillow Block Bearing Sizes Are Measured and Classified
A pillow block bearing — also called a plummer block or housed bearing unit — consists of an insert bearing mounted inside a cast iron, cast steel, or polymer housing with a flat base and two bolt holes. The size designation follows the inner ring bore diameter because that dimension determines shaft compatibility, which is the primary engineering constraint in any application.
The most widely used classification system uses a two-digit series number to encode the bore. For example, a bearing designated UCP 205 uses a P205 insert bearing with a 25 mm bore, housed in a UC-style cast iron pillow block. The "205" suffix means the bore is 5 × 5 = 25 mm. This formula (last two digits × 5) applies to bearings from the 04 series upward; sizes 00, 01, 02, and 03 correspond to 10 mm, 12 mm, 15 mm, and 17 mm respectively.
Standard Metric Bore Sizes by Series
The following table shows the most common metric bore diameters found in the 200 and 300 series, which are the workhorse series in most industrial and agricultural applications.
Standard metric bore sizes for 200 and 300 series pillow block bearings
| Bearing Code |
Bore Diameter (mm) |
Shaft Size (in) |
Typical Housing Width (mm) |
| UCP 200 |
10 |
— |
31 |
| UCP 201 |
12 |
— |
31 |
| UCP 202 |
15 |
— |
35 |
| UCP 203 |
17 |
— |
35 |
| UCP 204 |
20 |
— |
38 |
| UCP 205 |
25 |
— |
42 |
| UCP 206 |
30 |
— |
47 |
| UCP 207 |
35 |
— |
52 |
| UCP 208 |
40 |
— |
58 |
| UCP 209 |
45 |
— |
62 |
| UCP 210 |
50 |
— |
67 |
| UCP 212 |
60 |
— |
78 |
| UCP 215 |
75 |
— |
95 |
| UCP 218 |
90 |
— |
112 |
| UCP 220 |
100 |
— |
124 |
Inch-Series Pillow Block Bearing Sizes for North American Applications
While metric series dominates global manufacturing, the inch-series pillow block bearing remains heavily used across North America, particularly in agricultural equipment, food processing machinery, and legacy industrial systems. Inch-series units use a different designation format: the bore is expressed in fractions or decimals of an inch rather than millimeters.
Common bore sizes in inch series run from 1/2 inch through 3 inches, with 3/4", 1", 1-1/4", 1-1/2", 1-3/4", 2", 2-3/16", 2-7/16", and 2-15/16" being the most frequently ordered. The 1" and 1-1/2" sizes account for a disproportionate share of sales because they fit the drive shafts used in conveyor systems, augers, and fan assemblies throughout North American industry.
1/2"
Light Duty
Used in small conveyors, light fans, and instrumentation. Load capacity typically under 1,500 lbf dynamic.
1"
Most Common
Standard for mid-range conveyors, augers, pumps. Dynamic load ratings 3,000–5,000 lbf depending on series.
1-1/2"
Heavy Conveyor
Widely used in agriculture and packaging lines. Dynamic capacities reach 6,500–9,000 lbf in 300 series housings.
2-7/16"
Heavy Industrial
Typical for grain elevators, heavy fans, and industrial drives. Bolt hole spacing scales to 9"+ centers.
One critical note: inch-series and metric-series housings are not interchangeable even when the bore is very close in dimension. A 25 mm bore metric insert will not seat correctly in an inch-series housing designed for a 1" bore, because the outer ring diameter and locking geometry differ by manufacturer specification.
Full Dimensional Specifications Beyond Bore Diameter
Bore diameter tells you whether the bearing fits the shaft. But four other dimensions determine whether the bearing fits your machine — and engineers frequently overlook all four until they have a unit in hand that won't bolt down.
H — Base to Shaft Center Height
This is the distance from the bottom of the housing base to the centerline of the bore. For a UCP 205 (25 mm bore), H is typically 47 mm. For a UCP 210 (50 mm bore), H rises to approximately 65 mm. If you are replacing a bearing in a machine where the shaft height is fixed, H must match exactly or the shaft alignment will shift.
L — Bolt Hole Spacing (Center to Center)
The distance between the two mounting bolt holes measured center-to-center along the length of the housing. A UCP 205 typically has L = 95 mm; a UCP 210 steps up to approximately 130 mm. Mismatched bolt spacing is the primary cause of failed drop-in replacements.
N — Bolt Hole Diameter
The diameter of the mounting bolt holes. Most 200-series metric pillow blocks accept M12 bolts (12 mm bolt hole); 300-series and larger metric units step up to M16. Inch-series units typically use 1/2" or 5/8" bolt holes. Always verify N matches your mounting hardware before ordering.
B — Housing Width
The overall width of the bearing housing from face to face. This dimension determines whether the bearing fits within the available frame width. On a UCP 205, B is approximately 42 mm. On a UCP 215 (75 mm bore), B grows to around 95 mm.
A — Overall Length
The end-to-end length of the housing. This dimension matters when multiple pillow block bearings are spaced along a shaft and the available mounting surface is limited. Always check A against your frame layout before finalizing a bearing selection.
Load Ratings by Bearing Size: Dynamic and Static Capacity
Every bearing size carries a published dynamic load rating (C) and static load rating (C0). These values determine service life under actual operating conditions. The dynamic rating predicts how long the bearing will last at a given load and speed; the static rating sets the maximum load the bearing can withstand without permanent deformation of the raceways.
For a standard UC 205 insert bearing (25 mm bore) used in a UCP 205 pillow block, typical values are C = 14.0 kN and C0 = 7.80 kN. Scale up to a UC 210 (50 mm bore) and the values jump to C = 35.0 kN and C0 = 23.2 kN. The relationship is not linear — doubling the bore roughly triples the load capacity in most series because the rolling element diameter and number of balls both increase.
Representative dynamic and static load ratings for UC-series insert bearings by bore size
| Bearing |
Bore (mm) |
Dynamic C (kN) |
Static C0 (kN) |
Max Speed (rpm) |
| UC 204 |
20 |
12.8 |
6.55 |
1,800 |
| UC 205 |
25 |
14.0 |
7.80 |
1,600 |
| UC 206 |
30 |
19.5 |
11.2 |
1,400 |
| UC 208 |
40 |
25.5 |
15.3 |
1,200 |
| UC 210 |
50 |
35.0 |
23.2 |
1,000 |
| UC 212 |
60 |
47.5 |
32.5 |
900 |
| UC 215 |
75 |
66.0 |
48.0 |
750 |
| UC 218 |
90 |
96.0 |
72.0 |
600 |
| UC 220 |
100 |
112 |
86.5 |
530 |
Notice the speed trade-off: as bearing size increases, the maximum allowable speed drops significantly. A UC 204 can run at 1,800 rpm without special provisions; a UC 220 is limited to 530 rpm at similar load factors. Applications requiring both high load and high speed — such as high-speed conveyor drives — must use precision-grade bearings or different bearing types entirely.
Housing Series and Their Impact on Overall Bearing Dimensions
The same insert bearing can be fitted into different housing series, changing the overall unit dimensions without changing the bore. This matters more than most buyers realize. A UC 206 insert (30 mm bore) fits both a standard P206 housing and a heavy-duty PH206 housing, but the PH206 housing is significantly larger, heavier, and has wider bolt hole spacing — making it entirely different from a dimensional standpoint even though the bore matches.
200 Series Housing
- Lightweight cast iron
- Compact footprint
- Standard for light to medium loads
- Lower bolt hole load rating
- Most economical option
- Widely available off-the-shelf
300 Series Housing
- Heavier-duty cast iron or ductile iron
- Larger base dimensions
- Higher bolt hole capacity
- Used in agriculture and heavy conveying
- Wider bolt centers add stability
- Heavier and more costly than 200 series
Stainless / Polymer Housing
- Corrosion-resistant for food/wet environments
- Dimensions match metric standards
- Lighter weight than cast iron
- Lower maximum loads than iron housings
- Premium pricing versus standard housings
- Required for USDA/FDA-compliant installations
How to Select the Correct Pillow Block Bearing Size in 5 Steps
Getting the size right the first time saves both money and downtime. Follow this sequence for any new application or replacement job.
- Measure the shaft diameter precisely. Use a micrometer, not a tape measure or caliper. Shaft diameters must match bore diameter to within standard tolerance (h6 or j6 for most metric press-fit applications). A nominal 25 mm shaft may actually measure 24.97–25.00 mm; the bearing bore will be 25.000–25.013 mm for a normal clearance fit.
- Calculate the radial load on the bearing. Add up the weight of the shaft assembly, the belt or chain tension if applicable, and any process loads. Apply a service factor of 1.2 to 2.0 depending on shock loading severity. The resulting equivalent radial load must be below the bearing's dynamic rating C for the required service life.
- Verify the operating speed. Cross-reference your operating rpm against the bearing's speed rating. If you need to run at 1,200 rpm with a 50 mm bore, a standard UC 210 is adequate; a 100 mm bore unit of the same series is not, as its rated speed is only 530 rpm.
- Check housing dimensions against mounting surface. Measure or design the base-to-center height H and bolt center spacing L before ordering. Many failed replacements occur because the engineer ordered a bearing that fits the shaft but not the frame.
- Consider the environment. Standard cast iron housings are adequate for dry indoor applications. Food processing, marine, or chemical environments require stainless housings. High-temperature applications above 120°C require special greases and expanded internal clearance (C3 or greater).
Replacement Pillow Block Bearings: Cross-Reference and Interchangeability
One of the practical advantages of the pillow block bearing market is that ISO standardization means most housings from major manufacturers are dimensionally interchangeable within the same series. A UCP 205 from NSK, SKF, Dodge, Timken, or any ISO-compliant Chinese manufacturer will share the same bore diameter, housing footprint, bolt hole spacing, and shaft center height — you can swap one brand for another without redesigning the mounting.
However, interchangeability has limits. Insert bearings from different manufacturers should not be mixed into housings they were not designed for if you require precision fits. Discount insert bearings sold at significantly below-market prices often have outer ring diameter tolerances that are looser than specification, causing fretting in the housing bore. This produces noise, vibration, and eventual housing damage that negates any savings on the bearing itself.
Common Cross-Reference Designations
When cross-referencing bearing numbers across brands, keep the following equivalencies in mind:
- UCP 205 (generic) = P205 (Dodge/Baldor) = FYJ 25 TF (SKF) = UCPA205 (NSK regional variant)
- UCP 206 (generic) = P206 (Dodge) = SY 30 TF (SKF) — all with 30 mm bore
- UCP 210 (generic) = P210 (Dodge) = SY 50 TF (SKF) — all with 50 mm bore
- UCPX 05 (extended inner ring) is not interchangeable with standard UCP 205 — the wider inner ring changes the housing seat requirements
Always verify H, L, N, and B dimensions from the manufacturer's catalog rather than assuming cross-reference equivalency translates to dimensional identity. Catalogs from SKF, NSK, Timken, and Rexnord are freely available online and include full dimensional tables for every bearing size they produce.
Application-Specific Bearing Size Recommendations by Industry
Different industries have settled on specific pillow block bearing sizes as de facto standards based on decades of application experience. Understanding these patterns can guide your initial selection even before you run a full load calculation.
Agriculture and Grain Handling
Auger drives and grain elevator legs most commonly use 1" to 1-7/16" inch-series pillow block bearings or their metric equivalents (25–35 mm bore). Combine headers typically use 1-3/16" and 1-7/16" units. Grain dryers with high-temperature zones require bearings with C3 clearance and high-temperature grease rated above 150°C.
Food and Beverage Processing
FDA-compliant installations use stainless steel housings with food-grade NSF H1-approved grease. Bore sizes from 25 mm to 50 mm (UCP 205 through UCP 210) cover the majority of conveyor and mixer shaft applications. Sealed-for-life insert bearings eliminate relubrication intervals that create contamination risk.
Mining and Heavy Industry
Crusher feed conveyors and screen shaft applications regularly require 75 mm to 100 mm bore pillow block bearings (UCP 215 to UCP 220 or 300-series equivalents). These applications demand heavy-duty ductile iron housings with field-replaceable seals and grease fittings. Impact loads require a service factor of 2.0 or higher applied to dynamic load calculations.
HVAC and Fan Applications
Commercial fan shafts use 1" to 2-7/16" pillow block bearings depending on fan diameter and static pressure. Bearings in this service run continuously at moderate speeds with relatively low radial loads but benefit from precision-ground inserts to reduce noise. Extended inner ring variants (UCPX or UCPW series) are commonly used to accommodate shaft keys and set screws at specific distances from the fan wheel.
Practical Tips for Ordering and Installing Pillow Block Bearings by Size
Getting the size specification right is only half the job. Ordering errors and installation mistakes account for a significant share of premature bearing failures in the field. These practical notes apply regardless of the specific size you have selected.
01
Always Measure the Existing Unit Before Ordering a Replacement
If the old bearing's data plate is missing or illegible, measure the shaft diameter, the bolt center spacing L, and the base-to-shaft-center height H. These three measurements uniquely identify the housing series in most standard catalogs. Do not rely on the machine drawing if the machine is more than 10 years old; drawings are often not updated after field modifications.
02
Tighten Set Screws to Specification
Set screws on the eccentric locking collar or dual-set-screw style must be torqued to specification. Under-tightening allows fretting motion between shaft and bore that destroys the shaft surface within weeks. Over-tightening distorts the inner ring bore, reducing radial clearance and causing premature fatigue. For a 25 mm bore bearing, typical set screw torque is 10–12 Nm; for a 50 mm bore unit, the figure rises to approximately 20–25 Nm.
03
Verify Shaft Hardness for Set Screw Locking Designs
Set screw locking relies on the screw biting into the shaft surface to create mechanical lock. This only works reliably when shaft hardness is below approximately 250 HB (25 HRC). Shafts that are induction-hardened or through-hardened above this level will not develop adequate grip, and the bearing will walk on the shaft under load. In such cases, use adapter sleeve or eccentric collar locking designs instead.
04
Do Not Mix Grease Types When Relubrication
Most pillow block bearings are pre-greased with lithium complex grease at the factory. Adding incompatible grease — such as a calcium-based or polyurea-based product — causes the grease matrix to break down, resulting in rapid oil separation and bearing starvation. If you do not know what grease is already in the bearing, purge it completely with fresh compatible grease through the grease fitting until new grease appears at the seals before returning to service.
Frequently Asked Questions About Pillow Block Bearing Sizes
What is the most common pillow block bearing size?
In metric applications, the UCP 205 (25 mm bore) and UCP 206 (30 mm bore) are the highest-volume sizes globally due to their prevalence in conveyor systems, agricultural equipment, and light industrial machinery. In inch-series markets, the 1" bore unit is the single most common size ordered in North America.
Can I use a larger pillow block bearing than required?
Technically yes, if the shaft can be stepped up in diameter and the housing dimensions fit the mounting surface. In practice, upsizing a bearing adds cost and weight without proportional benefit. More importantly, oversized bearings often run at speeds below their minimum recommended speed, which prevents proper lubrication film formation and can actually reduce service life compared to a correctly sized bearing.
How do I read a pillow block bearing part number?
A typical designation like UCP 207-20 breaks down as: UC = bearing type (insert/self-aligning ball bearing); P = housing type (pillow block with flat base); 2 = series (200 series light to medium duty); 07 = bore code (7 × 5 = 35 mm, but check manufacturer table for accuracy); -20 = suffix for inch bore variant (20/16 = 1-1/4" bore). Suffixes after the main number vary by manufacturer and may indicate extended inner ring, stainless housing, food-grade seals, or special clearance classes.
What is the difference between UC 200 and UC 300 series?
The 200 series uses a lighter, more compact outer ring geometry with a smaller OD relative to bore diameter. The 300 series has a larger OD, more rolling elements, and higher load ratings. For the same bore size, a 300-series insert in a 300-series housing offers roughly 20–40% higher dynamic load capacity than the 200-series equivalent, at the cost of a larger and heavier unit.
Are metric and inch pillow block bearings the same dimensions?
No. A metric 25 mm bore bearing and an inch 1" bore bearing (25.4 mm) have different outer ring diameters and different housing geometries. They are not interchangeable. Additionally, the bolt hole spacings and base-to-center heights differ between metric and inch housings even when bore sizes are nearly identical. Always specify the exact bore diameter and series when ordering.
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