Insert Bearings

What is an insert bearing?

An insert bearing, also called a Y-bearing or bearing insert, is a ball bearing designed to be fitted into a housing and mounted directly onto a shaft. It is based on a sealed single-row deep groove ball bearing, but with a few important differences, such as the outer ring having a spherical outside surface, which lets the bearing swivel slightly in a matching housing to correct initial misalignment. The inner ring is usually extended on one or both sides to give room for a locking device that secures the bearing to the shaft. It comes fitted with seals, often combined with a flinger, and is pre-filled with grease.

Insert bearings are usually fitted into a housing to form a complete bearing unit, such as a pillow block (plummer block) or a flanged unit, which bolts onto a machine frame. The inner ring is normally a sliding fit on the shaft and is secured by a locking method rather than a press fit so that units can be fitted quickly without pressing tools. 

Why are insert bearings essential?

They make mounting a shaft quick and simple. A complete unit can be bolted to a frame, slid onto a shaft and locked in place, often in minutes. No precision-machined housing bores or shaft shoulders are needed, which saves design work and manufacturing cost. They tolerate initial misalignment between the shaft and the mounting surface, which is common on welded frames and long shafts, because the spherical outer ring can swivel in the housing during installation.

Insert bearings work on shafts with wider tolerances than conventional bearings require, including commercial drawn shafting, which reduces cost. Integrated seals protect against dust, dirt, and moisture, so they suit demanding environments. Many units can also be relubricated through a grease nipple in the housing. Replacement is straightforward. A worn insert can often be removed from its housing and replaced on its own, without changing the whole unit.

Typical applications include:

• Conveyors and material handling equipment
• Agricultural machinery
• Food and beverage processing equipment
• Packaging machinery
• Fans and air-handling units
• Textile and woodworking machinery
• Construction and mining equipment
• General-purpose shafts and rollers

The main types of insert bearings

Insert bearings are mainly classified by how they lock to the shaft.

• Grub screw (set screw) locking - Two grub screws, usually spaced 120° apart in the extended inner ring, are tightened onto the shaft. This is the most common and simplest type, and it works with rotation in both directions. 
• Eccentric locking collar - the inner ring has an eccentric (off-centre) extension that engages with a matching collar. The collar is turned in the direction of shaft rotation until it grips, then secured with a grub screw. It is best suited to applications with a constant direction of rotation, and it is generally not recommended where rotation regularly reverses.
• Adapter sleeve (tapered bore) - The bearing has a tapered bore and is mounted on a split, tapered adapter sleeve, which is tightened with a lock nut. This gives a firm, concentric grip on the shaft without marking it, so it suits heavier loads, higher speeds, and vibration. It takes more care and time to fit than grub screw or eccentric collar types. 
• Concentric locking - Some manufacturers offer systems in which a collar or sleeve clamps the inner ring evenly around the shaft. These give a concentric fit with less shaft damage than grub screws, and they work with rotation in both directions. 
• Plain bore with interference fit - this is less common and is used where the bearing is pressed onto the shaft rather than locked. 

Material and seal variants include:

• Stainless steel inserts - for washdown, food processing, and corrosive environments
• Inserts with heavy-duty or multiple lip seals - for very dirty or wet conditions
• High-temperature inserts with heat-resistant grease, seals, and cages
• Inserts with food-grade grease
• Non-relubricable inserts sealed for life, as well as relubricable versions with a lubrication hole in the outer ring

Common housing types that inserts are fitted into include:

• Pillow blocks (plummer blocks) - these mount on a base parallel to the shaft
• Square four-bolt flanged housings
• Oval two-bolt flanged housings
• Round flanged housings - often with a centring spigot
• Take-up housings - these slide in a frame to adjust belt or conveyor tension

Common housing materials include:

• Grey cast iron - this is the most common for general use
• Pressed steel - pressed steel is a lightweight and economical choice for light loads
• Stainless steel - for corrosive and hygienic environments
• Thermoplastic (polymer) - for food processing, washdown, and corrosion resistance

How to choose the right insert bearing?

• Shaft size - match the bore to the shaft diameter, in either metric or imperial. Check the recommended shaft tolerance in the manufacturer’s catalogue, as insert bearings accept wider tolerances than standard bearings, but limits still apply.
• Locking method - Choose grub screws for simple, economical mounting with rotation in either direction. Choose an eccentric locking collar for constant one-way rotation. Choose an adapter sleeve or concentric locking for higher speeds, heavier loads, vibration, or where the shaft must not be marked.
• Load and speed - check the dynamic and static load ratings and the speed limits in the catalogue. The permissible speed for grub screw and eccentric collar types often depends on the shaft tolerance, with tighter tolerances allowing higher speeds.
• Housing type - choose a pillow block for mounting on a surface parallel to the shaft. Choose a flanged housing for mounting on a surface perpendicular to the shaft, such as a frame wall; choose a take-up unit where tension needs adjusting. 
• Environment - use cast iron for general industrial use; use stainless steel or thermoplastic housings with stainless inserts for washdown, food processing, or corrosive conditions.
• Lubrication - choose relubricable units for heavy loads, high temperatures, contamination, or continuous operation. Also choose sealed-for-life units where relubrication is impractical or the duty is light.
• Misalignment - insert bearings compensate for initial misalignment during installation, but they are not designed to handle continuous angular movement in operation.
• Interchangeability - check that the insert’s outer diameter and spherical profile match the housing, particularly when mixing brands. 

Essential references and specialised ranges

Widely used industry designations:

• UC - insert with grub screws and an inner ring extended on both sides
• SB - insert with grub screws and a narrower inner ring extended on one side
• SA - insert with an eccentric locking collar and an inner ring extended on one side
• UK - insert with a tapered bore, used with an adapter sleeve

SKF designations for its Y-bearings include:

• YAR - grub screws, inner ring extended on both sides
• YAT - grub screws, inner ring extended on one side
• YET - eccentric locking collar, inner ring extended on one side
• YEL - eccentric locking collar, inner ring extended on both sides
• YSA - tapered bore for adapter sleeve mounting

How UC numbering works:

The first digit after UC indicates the series (2 is the most common light series), and the last two digits give the bore using the same system and deep groove ball bearings.

Common metric references:

• UC201 - 12mm bore
• UC202 - 15mm bore
• UC203 - 17mm bore
• UC204 - 20mm bore
• UC205 - 25mm bore
• UC206 - 30mm bore
• UC207 - 35mm bore
• UC208 - 40mm bore
• UC209 - 45mm bore
• UC210 - 50mm bore

UC201 to UC204 share the same outer diameter (47mm), so they all fit the same size of housing; imperial bores are shown by a suffix in sixteenths of an inch. For example, UC205-16 has a 1" bore (16/16), and UC205-14 has a 7/8" bore (14/16). 

Common housing prefixes:

• P - pillow block
• F - square four-bolt flange
• FL - oval two-bolt flange
• FC - round flange with centring spigot
• T - take-up unit
• PA - pillow block with a tapped base

Specialised ranges:

• Stainless steel and thermoplastic units for food, beverage and pharmaceutical processing
• Units with food-grade grease and washdown-resistant seals
• Heavy-duty sealed units for agriculture, quarrying and mining
• High-temperature units for ovens, kilns and dryers
• Low-friction units for fans and light, high-speed applications
• Units with protective end covers, which improve safety and keep out contamination

FAQ - All you need to know about insert bearings

What is the difference between an insert bearing and a bearing unit?

The insert is the bearing itself, and the bearing unit is the insert fitted into a housing, such as a pillow block or flange, ready to bolt in place.

Can I replace just the insert?

Yes, in most cases. The insert can usually be swivelled out of the housing through the housing’s loading slots and replaced with a new one of the same reference. If the housing is cracked, worn, or corroded, replace the whole unit.

Can insert bearings compensate for misalignment?

Yes, but only initial misalignment, such as slight errors in the frame or mounting surfaces. The spherical outer ring lets the insert settle at the correct angle during installation. They are not designed for misalignment that keeps changing during operation.

Do insert bearings need greasing?

Sealed-for-life inserts don’t need relubricating, but relubricable units should be greased through the grease nipple at intervals recommended by the manufacturer, using a compatible grease. Avoid over-greasing, as excess pressure can damage or push out the seals. Add grease slowly, ideally while the shaft is turning slowly. 

Why is my insert bearing noisy or running hot?

Common causes include:

• A loose locking device, which allows the inner ring to creep on the shaft
• Contamination entering past damaged seals
• Too little or too much grease
• Excessive load or speed
• An incorrectly aligned or poorly supported shaft