Shaft clearance in a plain bearing installation is the difference between which two dimensions?

• A. Bearing bore and housing bore
• B. Shaft diameter and bearing bore
• C. Shaft diameter and outer diameter
• D. Bearing inner diameter and outer diameter

Answer: (B)

In a plain bearing setup, the gap that allows the shaft to rotate is defined by the difference between the shaft diameter and the bearing bore diameter. The bearing’s inner bore must be slightly larger than the shaft so there’s a small clearance for motion and lubrication. The radial clearance is roughly half of that difference, since the gap sits around the shaft on all sides.

If the bore is smaller than the shaft, you get an interference fit and binding. If the bore is much larger than the shaft, there’s excessive play and reduced control of alignment. The other dimensions mentioned relate to different interfaces (bearing bore to housing, shaft to outer components, or the bearing itself) and do not describe the shaft clearance.