Mounting bearings with a cylindrical bore

by Kevin Sweeney
21 February, 2024
10 min read

Generally bearings will have a cylindrical or tapered bore. Cylindrical bores rule the day but Taper bores are not uncommon and usually follow a 1:12 taper.

Understanding the Basics of Mounting Bearing with a cylindrical bore

Non-separable bearings are bearings which cannot be taken apart without tools.

With non-separable bearings, the ring that requires the tighter fit is usually mounted first. It could be the housing or the shaft which is fitted first depending on the designer’s instructions. 

Non-separable bearings are the most common type where the bearing inner and outer ring are a fixed unit composed of inner and outer rings, balls or rollers, cage and seals. 

Separable bearings are bearings where the rings can be taken apart prior to use and assembled onto or into the application in pieces.

With separable bearings, the inner ring can be mounted independently of the outer ring, which simplifies mounting, especially  when both rings require an interference fit. 

Alignment is critical when mounting the shaft and inner ring assembly into the housing containing the outer ring.  You want  to avoid scoring the raceways and rolling elements. When mounting cylindrical or needle roller bearings with an inner ring without flanges or with a flange on one side only, a guiding sleeve should be used. The outside diameter of the sleeve should match the raceway diameter of the inner ring and be machined to the tolerance class d10Ⓔ for cylindrical roller bearings. The tolerance of 0/–0,025 mm is required for needle roller bearings.

Cold mounting means installing the bearings at the ambient temperature without the need for heating or cooling.

For normal fits standard bearings can be installed by applying light hammer blows to a bearing fitting tool The tool enables the mounting force to be applied centrally. The fitting tool is crucial for alignment.

When a bearing needs to be pressed onto the shaft and into the housing bore at the same time, the mounting force must be applied equally to both rings and the abutment surfaces of the mounting tool must lie in the same plane. Fitting tools are available from Pacific International Bearing Sales Inc.

With self-aligning bearings, the use of an intermediate mounting ring prevents the outer ring from tilting when the bearing and shaft assembly is fitted into the housing bore . The balls of larger self-aligning ball bearings in the 12 and 13 series extend from the faces of the bearing, meaning the mounting ring must have a recess.

FAG self aligning ball bearing

Hot mounting

It is not possible to mount larger bearings without heating. Using an FAG Bearing Induction  heater for large  bearing mounting will ease the process.The force required to mount a bearing increases considerably with increasing bearing size. See link on how to use heat for mounting and removing bearings.

The required difference in temperature between the bearing ring and shaft or housing depends on the degree of interference and the diameter of the bearing seat. Open bearings must not be heated to more than 120 °C (250 °F). Bearing Manufacturers do not recommend heating bearings capped with seals or shields above 80 °C (175 °F). If higher temperatures are present make sure that the temperature does not exceed the permissible temperature of either the seal or grease, whichever is lowest.

When heating bearings, overheating must be avoided. To heat bearings evenly and reliably, PIB recommends using FAG electric induction heaters. If hotplates are used, the bearing must be rotated  a number of times. Sealed bearings should never contact the heating plate directly. It is a good practice to place a ring between the plate and bearing.

Before mounting the bearings ensure the shaft and housing are clean and free from imperfections. The dimensions of the shaft and bore must match the bearing’s specified tolerances for the correct fit. The bearing itself should be inspected for any damage or defects before installation. Depending on the fit type, either press fitting or thermal fitting is used for mounting, ensuring the force is applied evenly and directly to the appropriate ring. After installation, it’s important to check for smooth operation and proper alignment, followed by adequate lubrication according to specifications. 

The final step involves a comprehensive inspection and functional testing under load to confirm correct installation and performance. This detailed approach guarantees the bearing’s optimal functionality and longevity in its mechanical application.

Identify the cylindrical bore on a bearing?

Fig 1. Inner ring 2. Balls 3. Retainers 4. Inner ring (bore) is cylindrical 5. Retaining clip

The bore on a bearing refers to the inner diameter of the bearing’s inner ring. This dimension in the bearing design determines the fit between the bearing and the shaft it’s mounted on. In cylindrical bore bearings, this inner diameter is shaped as a perfect cylinder, designed to match and fit precisely onto a cylindrical shaft. The accurate measurement and manufacturing of the bore are essential for ensuring a proper fit, which in turn affects the bearing’s performance, lifespan, and efficiency in mechanical applications. This dimension is key in bearing selection and application, ensuring compatibility with the machinery’s shaft size and operational requirements.

Types bearings with cylindrical bores

Single row radial ball bearings Series 600, 6000, 6200, 6300 and 6400 are the most common types of bearings. Applications are endless but commonly found in electric motors, hand tools, automobiles and much much more.

Buy Standard single row radial ball bearings.

Single  and Double Row Cylindrical Roller Bearings with cylindrical bores

These bearings are designed for applications requiring high radial load capacity. They’re commonly used in electric motors, automotive applications, and general industrial machinery. Double row versions  have two rows of rollers which allow them to carry more radial load and offer greater rigidity. They are suitable for applications like machine tool spindles where heavy radial loads are prevalent.

To buy high precision cylindrical roller bearings or go to our site to see all types and sizes of bearings available with both cylindrical and tapered bores.

Generally accepted  step-by-step guide how to mount  bearings with cylindrical or tapered bores


The preparation step involves thoroughly cleaning the shaft and housing to remove all dirt, grease, and debris. This step is essential because any contaminants can affect the bearing’s fit and function. Additionally, a detailed inspection of the shaft and housing is necessary to identify and rectify any surface imperfections like nicks or burrs. These imperfections, if left unchecked, can lead to misalignment or premature bearing failure. Proper preparation sets the foundation for a smooth installation process.


The inspection step involves a meticulous examination of the bearing for any signs of damage or manufacturing defects. This check ensures the integrity and functionality of the bearing. Additionally, it’s vital to measure the bearing’s dimensions accurately and verify that they match the specifications of the shaft and housing. This step ensures compatibility and a correct fit, which is essential for the bearing’s optimal performance and longevity in its application.


Misalignment, even if slight, can lead to uneven load distribution, increased friction, and premature wear or failure of the bearing. The bearing should be positioned carefully and precisely on the shaft, verifying that it is straight and aligned correctly. This step requires a keen eye and careful handling to ensure that the bearing is seated properly, ensuring smooth operation and longevity of the bearing in its mechanical application.

Mounting method

Choosing the correct mounting method for cylindrical bore bearings depends on the fit type:

  • Interference Fits: In cases where the bearing fit is tight (interference fit), heating the bearing can be an effective method. This process involves gently heating the bearing to expand its inner diameter, allowing it to slide onto the shaft more easily. Care must be taken to heat the bearing evenly and not exceed recommended temperatures, as excessive heat can alter the bearing’s properties.
  • Clearance Fits: For applications with a loose fit (clearance fit), a press or a specialized mounting tool is used. This method involves applying even pressure to fit the bearing onto the shaft without damaging it. The pressure should be applied directly to the ring being mounted to avoid exerting force through the rolling elements.

Force Application

The force must be applied evenly and directly to the ring being mounted. If mounting the inner ring, the force should be directed on the inner ring only. Similarly, for the outer ring, apply force on the outer ring. This ensures that the rolling elements are not damaged and the bearing maintains its integrity and functionality. Careful and precise application of force is key to a successful bearing installation.


After installation, the bearing should be lubricated by the manufacturer’s specifications. The type of lubricant used (oil or grease), along with the quantity and application method, should be carefully chosen based on the bearing type and its operational conditions. Proper lubrication ensures smooth operation and can prevent overheating and corrosion, which are critical for maintaining the bearing’s performance and reliability.

Final Inspection

This inspection involves verifying that the bearing is correctly seated and aligned on the shaft, ensuring there’s no play or misalignment. Additionally, the bearing should be manually rotated to check for smooth operation, ensuring there are no signs of binding or roughness, which could indicate an issue. This thorough inspection is key to confirming the integrity and proper functionality of the bearing installation.

For a comprehensive selection of bearings and expert advice on their installation and use, please visit Pacific International Bearing Sales. Our website online catalog offers an easy-to-navigate shop where you can conveniently place orders for high-quality bearings tailored to your specific needs.

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Written by

Kevin Sweeney

Founder and CEO at Pacific International Bearing Sales Inc (PIB)
Education: BS Business and Economics California State University Hayward Ca
CBS (Certified Bearing Specialist)

My role with Pacific International Bearings (PIB) is currently CEO. Since 1976, I have been deeply involved in the bearing industry, working in manufacturing sales at NTN Bearing and subsequently in Bearing Distribution. Before establishing PIB in 1990, I gathered valuable experience in bearing manufacturing and distribution. The last 45 + years in the bearing industry have been both rewarding and challenging, assisting customers across a large number of diverse bearing applications.
Outside of the bearing industry, my interests are family, woodworking, motorcycling, cars, gardening, and golf.
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