Pillow Block Bearing Size Chart: How to Determine the Right Size for Your Shaft

The most common sizing mistake we see: someone measures their shaft with a tape measure, rounds to the nearest half-inch, and orders the wrong bore.

The bearing arrives, won't slide on cleanly, and they assume it's defective.

It's not—the shaft was 1.000" but they ordered a 1-1/16" bore.

Getting pillow block bearing size right starts with an accurate shaft measurement and ends with cross-checking three dimensions: bore, center height, and bolt spacing.

This guide walks through all of it, with complete size charts for UCP200 metric and imperial series.

How to Read a Pillow Block Bearing Model Number

Every UCP model number encodes the housing type, series, bore size, and—for inch variants—the exact shaft diameter.

Once you know the pattern, you can decode any unit in seconds.

Take UCP205-16 as an example:

UC

Insert bearing type (wide inner ring, set screw)

P

Pillow block housing

2

200 series (light-to-medium duty)

05

Bearing size code → bore = 05 × 5 = 25mm

-16

Inch bore suffix: 16/16 = 1.000 inch

Metric vs Imperial Suffixes

Units without a suffix (e.g. UCP205) are metric—bore is 25mm. Units with a numeric suffix are inch bore—the suffix is the bore in 1/16 inch increments.

So UCP205-14 has a bore of 14/16 = 7/8 inch, and UCP205-16 has a 1-inch bore.

✅ Quick bore calculation for metric units

For UCP204 onward, the bore in mm = last two digits × 5.

So UCP204 = 20mm, UCP205 = 25mm, UCP206 = 30mm, UCP207 = 35mm, UCP208 = 40mm, and so on.

Note:

UCP201, UCP202, and UCP203 are exceptions—their bores are 12mm, 15mm, and 17mm respectively, not derived from the ×5 rule.

Other Common Prefixes

Key Dimensions Explained

UCP200 Series Size Chart (Metric)

The UCP200 series is the most widely used pillow block bearing series globally.

Bore sizes run from 12mm (UCP201) to 75mm (UCP215), covering the vast majority of industrial shaft diameters.

All dimensions below conform to ISO standards and are consistent across reputable manufacturers.

Source: industry-standard UCP200 series technical specifications. Dynamic load ratings (Cr) are for standard UC200 insert bearings. Highlighted rows = most commonly stocked sizes. Always verify with your supplier's specific catalog for tolerance details. 

Browse Lily Bearing's full UCP200 series range by bore size and material: Pillow Block Bearings — Product Range →

✅ Most commonly ordered metric sizes

UCP204 (20mm), UCP205 (25mm), UCP206 (30mm), UCP207 (35mm), and UCP208 (40mm) account for the majority of industrial orders.

If you're specifying a new design, using one of these five sizes gives you the widest supplier availability and fastest lead times.

UCP200 Series Size Chart (Imperial / Inch)

Imperial inch bore variants use a suffix indicating bore size in 1/16 inch increments.

A UCP205-16 has a 1-inch bore (16 × 1/16 = 1.000").

The housing dimensions are identical to the metric counterpart—only the bore changes.

Source: industry-standard UCP200 series technical specifications. Highlighted rows = highest search volume / most commonly ordered inch sizes. Housing dimensions are identical for metric and inch variants of the same bearing number. 

⚠️ Don't confuse UCP205-16 and UCP205-100

Both designate a 1-inch bore UCP205. The "-16" suffix means 16 × 1/16 = 1.000".

The "-100" suffix is an alternative designation used by some manufacturers for the same 1.000" bore.

They are the same bearing—just different catalog naming conventions.

Always confirm bore size in decimal, not just the suffix number.

UCP200 vs UCP300: Which Series Do You Need?

For the same shaft diameter, UCP300 series uses a larger bearing insert than UCP200, which means a bigger housing but higher load capacity.

Here's a direct comparison for a 25mm shaft:

For most conveyor, fan, and general industrial applications, UCP200 series is the right choice.

But knowing when to switch is just as important as knowing how to read the chart.

The practical trigger for moving to UCP300 is load, not preference.

When the equivalent dynamic load consistently exceeds 60–70% of the UCP200 unit's Cr rating—after applying your safety factor—you're running the bearing harder than it's designed for.

The UCP300 insert uses a larger ball complement and a bigger OD for the same bore, which gives you roughly 60% more load capacity (14.0 kN → 22.5 kN for a 25mm bore) at the cost of a taller, longer housing.

Speed is the other factor.

The larger rolling elements in UC300 series don't spin as fast—UC305 tops out around 4,500 rpm with grease versus ~5,850 rpm for UC205.

If your application needs both high speed and high load on the same shaft, you're looking at a different bearing category altogether, not just a series upgrade.

One practical note: UCP300 housings are not bolt-pattern compatible with UCP200.

The center height H and bolt spacing J are different, so you can't swap series without drilling new mounting holes.

Need help understanding load capacity calculations for your application? Load Capacity and Performance Analysis of Pillow Block Bearings →

Shaft Tolerance and Bore Fit

Pillow block bearing bore is manufactured to a specific tolerance.

The shaft needs to be within tolerance for the bearing to grip correctly—too loose and it spins on the shaft, too tight and you can't install it.

Recommended Shaft Tolerances for UCP Series

What Happens with the Wrong Shaft Tolerance

A shaft undersize by more than 0.05mm relative to the bore creates enough clearance for the inner ring to creep rotationally under load—called "shaft spinning."

This scores both the shaft and the bearing bore within hours of operation.

We've seen shafts that looked fine visually but had worn 0.08–0.10mm undersize from years of previous bearing contact; a new bearing on that shaft will fail just as fast as the old one did.

A shaft oversize by more than 0.025mm above the h6 upper limit makes installation extremely difficult and can crack the inner ring during assembly.

If the bearing won't slide on by hand with a thin oil coat, stop—don't force it.

For detailed H7 shaft tolerance standards and precision installation protocols: Mounted Bearing Installation: H7 Standards →

Surface Finish Requirements

The shaft surface finish in the bearing contact zone should be Ra ≤ 1.6 µm (63 µin).

In practice, what kills set screw grip isn't usually a shaft that was machined too rough—it's a shaft that's been in service long enough to develop circumferential scoring from a previous bearing that spun.

Those grooves don't look serious, but they give the set screws nothing to bite against.

A quick pass with fine emery cloth in the axial direction, not circumferential, is enough to restore a functional surface before installing a new unit.

3-Step Selection Process

Most selection errors happen because people jump straight to bore size and ignore the other two critical checks. Here's the complete process:

Final Thoughts

Thirty seconds with a micrometer prevents the most common mistake in this whole process.

After that it's three checks: bore match, load rating, housing footprint.

The size charts above cover the vast majority of what you'll encounter—if your shaft is between 12mm and 75mm metric or 1/2" to 3" imperial, there's a standard UCP unit for it.

If you're specifying a new design, lock in one of the five most common sizes (UCP204–UCP208) from the start.

Supplier availability is widest there, lead times are shortest, and replacement sourcing will never be a problem years down the line.

For housing material selection—cast iron, stainless steel, or thermoplastic: Cast Iron Pillow Block Bearings: Properties, Grades, and When to Choose One →

Technical note:

Dimension data in this article references industry-standard UCP200 series technical specifications, cross-referenced with ISO standard dimensions. Dynamic load ratings (Cr) are for standard UC200 series insert bearings under normal operating conditions. Always consult the specific manufacturer's catalog for your selected unit before finalizing a design. Lily Bearing assumes no liability for applications specified without consulting relevant manufacturer documentation.