A bearing block, most often called a pillow block, is a mounted unit with a bearing inside a bolted housing that supports a rotating shaft and reduces friction.
If you run a conveyor, fan, or any industrial line, you work with these components whether you call them bearing blocks, pillow blocks, or plummer blocks. The names get tossed around interchangeably, but engineers use them differently—and choosing the wrong type means equipment that fails under load. This guide covers the exact differences, how to install them, and what to look for when buying one.
What Exactly Is a Bearing Block?
A bearing block is a pre-assembled unit consisting of a bearing housed inside a casing that bolts onto a mounting surface. The bearing supports the shaft, reduces friction, distributes loads, and keeps everything aligned during operation. Most standard housings are made of cast iron for durability and high load-carrying capacity. Bearings inside are typically self-aligning ball bearings that compensate for minor angular misalignment, with set screws or locking collars to secure the unit on the shaft.
Pillow Block vs Plummer Block: What Is the Difference?
The terms overlap in casual use, but the engineering distinction matters. A pillow block is a light-duty unit, often with a one-piece housing and an integral bearing. A plummer block refers to a heavy or very heavy-duty housing that is always split into two pieces—a base bolted to the foundation and a cap that clamps down on the bearing and shaft. Using a light-duty pillow block where a two-piece plummer block is needed can lead to catastrophic housing failure under high loads.
Common Uses for Bearing Blocks
Bearing blocks show up in conveyors, fans, agricultural machinery, packaging lines, HVAC systems, and robotics. Their core purpose in every application is the same: keep the shaft spinning freely while holding it in place under load.
- Conveyors: support drive and idler shafts along the line
- Agricultural equipment: handle dusty, high-vibration environments
- HVAC systems: support fan and blower shafts
- Robotics (REV ION System): mount MAXSpline shafts rigidly using dedicated bearing blocks
How to Install a Bearing Block
Installation varies slightly by design, but the general sequence is the same for most industrial units. The REV ION Build System (used in FIRST Robotics) follows its own pattern because the blocks mount to extrusion with a specific hole pattern.
General industrial installation:
- Bolt the lower piece (or the full base) of the housing to the foundation or mounting plate. Make sure the surface is flat and clean.
- Rest the bearing and the shaft on the lower half. The bearing should seat into its pocket without force.
- Place the cap on top and tighten the bolts evenly to the specified torque. Over-torquing can distort the housing and bind the bearing.
REV ION System installation:
- Identify a surface with a 2-inch mounting hole pattern on the REV ION extrusion.
- Mount the MAXSpline Pillow Block or Bearing Retaining Plate (
REV-21-2286-PK10) to that surface. - Insert the MAXSpline Shaft (
REV-21-2520) into the bearing block. The block holds the shaft rigidly without precision machining.
the shaft rotates freely with no wobble or binding. If it feels tight, check that the housing bolts are not over-tightened and that the shaft is aligned square to the mounting surface.
Bearing Block Orientation: Parallel vs Right Angle
Pillow blocks mount parallel to the mounting surface—remember “P for parallel.” If your shaft needs to sit at a right angle to the surface, you need a flange block, not a pillow block. This is one of the most common installation mistakes, and it forces the bearing to carry loads it was not designed for.
When you are ready to buy, see our tested product roundup on the best bearing block and bushing options for industrial and robotics applications.
| Bearing Block Type | Housing Style | Typical Load Rating |
|---|---|---|
| Light-duty pillow block | One-piece, integral bearing | Low torque, light loads |
| Heavy-duty plummer block | Two-piece (base + cap) | Heavy to very heavy loads |
| Split pillow block housing | Modular two-piece for inch sizes | Medium to heavy loads |
| Flange block | Flanged for right-angle shaft | Light to medium loads |
| Take-up block | Adjustable positioning | Light to medium loads |
| REV ION MAXSpline block | Specifically for REV extrusion | Educational/robotics loads |
| SKF VRE3 plummer block | Unsplit housing, very high loads | Extreme loads |
How Do Bearing Blocks Reduce Friction?
The bearing insert inside the housing uses rolling elements—balls or rollers—between the shaft and the housing. This changes sliding friction (which generates heat and wear) into rolling friction, which is much lower. The self-aligning feature in most pillow blocks allows the bearing to compensate for small angular misalignments between the shaft and the housing, further reducing friction and extending service life. Proper alignment during installation is still critical because severe misalignment will overload even a self-aligning bearing.
Material and Mounting Mechanisms
Cast iron is the default material for standard bearing block housings because it absorbs vibration well and handles high loads. Mounting mechanisms vary by model: set screws lock the bearing directly onto the shaft, while locking collars create a tighter, more concentric grip. Bolt holes or slots in the base let you adjust position during installation.
| Mounting Mechanism | How It Works | Best For |
|---|---|---|
| Set screw | Screw tightens directly against shaft | Light-to-medium loads, easy adjustment |
| Concentric locking collar | Collar tightens evenly around shaft | Heavier loads, higher precision |
| Eccentric locking collar | Offset collar acts as cam | Space-constrained installations |
| Bolt hole mounting | Bolts through housing base into surface | Permanent or semi-permanent setups |
| Slide/slot mounting | Adjustable slots in base feet | Systems needing tension adjustment (conveyors) |
Common Mistakes When Using Bearing Blocks
- Confusing light-duty pillow blocks with heavy-duty plummer blocks. A one-piece pillow block on a high-load conveyor will crack. Always match the housing design to the load range.
- Installing for the wrong shaft orientation. Pillow blocks are for parallel shafts; flange blocks handle right-angle setups. Check your shaft angle before choosing.
- Ignoring the self-aligning limit. The bearing compensates for minor misalignment, not severe angular errors. Align the shaft to within the bearing’s specified tolerance.
- Loose mounting bolts. Any movement between the housing and the foundation causes vibration, wear, and eventual failure. Tighten to spec.
Safety and Compatibility Tips
Pillow blocks are built for low-torque, light-load applications unless the product sheet explicitly states a higher rating. A heavy load on a light-duty housing is a safety hazard—the housing can shatter. Cast iron withstands normal industrial environments but may corrode in wet or chemical-heavy settings; stainless alternatives exist but are less common. The REV ION MAXSpline Pillow Block is designed only for REV-21-2520 MAXSpline Shafts; it will not fit standard round shafts.
Checklist: Picking the Right Bearing Block
- Identify your load range—light, medium, heavy, or very heavy.
- Decide shaft orientation: parallel (pillow block) or right angle (flange block).
- Check whether a two-piece housing is needed for heavy loads.
- Verify the mounting hole pattern matches your surface.
- Confirm the shaft type (round vs. splined) and diameter.
- Select the locking mechanism (set screw or collar).
- Consider the environment—cast iron for dry indoor, stainless for wet/corrosive.
References & Sources
- Wikipedia. “Pillow block bearing.” Core definitions and design distinctions between pillow blocks and plummer blocks.
- SKF. “Pillow block ball bearing units.” Official product documentation for industrial mounted bearing units.
- REV Robotics. “Bearings / Bearing Blocks.” Official installation steps and model numbers for the REV ION Build System.
FAQs
Can you use a pillow block for vertical shaft mounting?
Standard pillow blocks are designed for horizontal shaft applications where the shaft runs parallel to the mounting surface. For vertical shafts or right-angle setups, use a flange block or a specialized vertical-mount pillow block. Installing a standard pillow block vertically can starve the bearing of lubrication and cause premature failure.
How do you know what size bearing block you need?
The size is determined by the shaft diameter, the load weight, and the mounting hole pattern on your surface. Measure the shaft diameter precisely, calculate the expected radial and axial loads, and check the manufacturer’s load rating tables for that shaft size. The housing’s base dimensions must match your mounting holes—do not enlarge holes to fit a mismatched block.
What lubrication do bearing blocks require?
Most pillow blocks come pre-greased from the factory and include a grease fitting for re-lubrication. The standard grease is lithium-based NLGI Grade 2 grease for general industrial use. High-temperature, food-grade, or waterproof greases are available for specialized environments. Follow the manufacturer’s relubrication interval—typically every 6 to 12 months under normal conditions.
Why is my bearing block making noise after installation?
Noise usually means misalignment, over-tightened housing bolts, or an undersized block for the load. First, check that the shaft runs straight into the bearing and that the housing bolts are torqued evenly to spec. If the noise persists, the bearing insert may be damaged from the installation—remove the block and spin the bearing by hand to feel for roughness.
Are bearing blocks interchangeable between manufacturers?
Bearing blocks follow standardized mounting dimensions (e.g., inch-based pillow block housings) for basic sizes, so a block from one manufacturer can often fit another brand’s bolt pattern. However, the bearing inserts themselves may use different locking mechanisms (set screw vs. collar) that are not interchangeable. Stick to one manufacturer for the complete unit when possible.