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Mounted Bearings — Pillow Blocks & Flange Units

Mounted bearings are bearings already fitted in a housing that bolts to a frame. This sheet covers pillow blocks, flange units and take-ups, the insert locking methods and how to read a common mounted bearing number.

Ref MRO-0009

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A mounted bearing unit is an insert bearing in a housing. The housing bolts to a frame or wall and the insert locks to the shaft. Mounted units are used on conveyors, fans, agricultural machinery, blowers and packaging equipment. Most inserts are wide-inner-ring ball bearings with a spherical outer ring, so they can self-align in the housing during mounting. Spherical roller and tapered roller inserts are used for heavier loads.

How to identify

Look at the housing shape. A pillow block sits on a base parallel to the shaft and bolts down with two or four bolts. A flange unit bolts to a wall square to the shaft with two, three or four bolts, or with a pilot. A take-up unit slides in a frame to adjust belt or conveyor tension. Then look at how the insert locks: set screws, an eccentric collar, a concentric collar or a tapered adapter. Read the number on the housing and the insert. A common naming style is UC for a set screw insert and UCP for the matching pillow block. On many inch inserts, a dash number shows the bore in sixteenths of an inch.

Housing styles

Style	Mounting	Common use	Notes
Two-bolt pillow block	Base, two bolts	Conveyors, fans, light industry	Most common style
Four-bolt pillow block	Base, four bolts	Heavier loads	Larger shaft sizes
Tapped base pillow block	Bolts from below	Tight spaces	Housing threaded
Two-bolt flange	Wall, two bolts	Light duty, ag equipment	Diamond shaped
Four-bolt flange	Wall, four bolts	General duty	Square shaped
Piloted flange	Wall, pilot locates the unit	Precise location	Needs a machined bore
Take-up unit	Slides in a frame	Conveyor tail pulleys	Match frame and bolt size
Hanger	Hangs from above	Screw conveyors	Specialty style

Locking methods

Method	How it holds	Notes
Set screw	Two screws in the inner ring	Simple; can mark the shaft
Eccentric collar	Cam collar locks in the direction of rotation	Lock in the direction the shaft turns
Concentric collar	Clamping collar	Less shaft damage; better balance
Tapered adapter	Sleeve wedges in the bore	For heavy and high-speed duty

Key points

Shaft size, housing style, center height and bolt spacing must all match the old unit.
Housing materials include cast iron, ductile iron, pressed steel, stainless and thermoplastic for washdown.
Set screw tightening values come from the bearing maker. Use the right hex key and torque.
Grease fittings, seals and covers change with the application. Ask about washdown, dust and temperature.

Common mistakes

Matching the insert bore but not the center height.
Locking an eccentric collar against rotation.
Using a pressed steel housing in heavy duty service.
Overgreasing sealed units.

Governing standards: No single standard is listed for this sheet. Use the maker's catalog for housing dimensions and interchange.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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