Shaft and Housing Fits

The ideal mounting for a precision bearing is line to line on both shaft and housing. Such a fit has no interference or looseness. For random fitting the fit tolerances may need to be increased to meet the lot variances. For selective fitting the bearing inner and outer diameter should be accurately measured, then the shaft and housing machined to suit.

Interference fits should be used with care as they can distort the raceway and reduce radial internal clearance. In preloaded pairs, reducing the internal radial clearance increases the preload. If excessive, the results can be significantly reduced speed capability and higher operating temperatures which will ultimately reduce life.

Some applications require interference fits such as:

  • Heavy radial loading
  • Intense vibration
  • Lack of axial clamping

Radial internal clearance is reduced by approximately 80% of the interference fit.

Interference fits are usually applied to the rotating ring.

Loose fits may be suggested when:

  • Axial clamping is possible, such a snap rings, locking collars or adhesive
  • Ease of assembly
  • Axial movement is required for spring preload or thermal movements

Fits are often overlooked and is arguably the most common bearing handling mistake.
The table below is simply a guideline as there are many influencing factors to be considered such as.

  • Load, speeds and temperatures
  • Ease of assembly and disassembly
  • Rigidity and accuracy requirements
  • Machining tolerances

Therefore the appropriate fit may fall somewhere in between.

ROTATING RING INNER RING OUTER RING
APPLICATION DESIRED FIT TYPE FIT(inches) USE SHAFT DIAMETER USE HOUSING DIAMETER
Low speed, or spring preload. Loose .0001L to .0005L d - .0003
d - .0005
D .0001
D .0003
Medium speed Line to Line .0002L to .0002T d - .0000
d - .0002
D - .0000
D - .0002
High speed Light press .0000 to .0004T d .0002
d - .0000
D - .0002
D - .0004
High speed, high load Tight press .0002T to .0006T d - .0002
d - .0004
D - .0004
D - .0006

STATIONARY RING INNER RING OUTER RING
Most applications
Line to line
to loose
.0000 to .0004L d - .0002
d - .0004
D - .0000
D .0002

L = Loose fit, T = Tight fit, d = Bearing I.D., D = Bearing O.D.