This cannot be a tight assembly; some ball-to-raceway clearance is necessary to make room for oil films and provide clearance for heat expansion of the balls at operating temperature. When a ball bearing’s inner race is pressed onto a shaft, it is expanded slightly and the outer race may be compressed a bit if pressed into a housing or clamped between crankcase halves. Because this may cause bearing internal clearance to disappear, replaced by preload, bearing failure can occur prematurely. To prevent this, bearings with increased internal clearance are made, identified as “C3” by marking on the faces of the outer race. Bearing size (such as 6005, 6305, etc.) is also marked on the outer race. Consult bearing catalogs for dimensions, installation advice, and other interesting information.