In a plain bearing installation, shaft clearance is defined as what?

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

Answer: (A)

The gap is the difference between the bearing bore and the shaft diameter. In a plain bearing, the shaft (journal) rotates inside the bearing bore, so the clearance is the diametral difference between those two surfaces. This space, often called the journal clearance, determines the oil film thickness and the ability to rotate smoothly without rubbing.

For example, if the bearing bore is 50.00 mm and the shaft diameter is 49.50 mm, the diametral clearance is 0.50 mm (giving about 0.25 mm radial clearance on each side). The other options mix in measurements like housing bore or outer diameters, which do not define the shaft clearance inside the bearing.