As a retired tradesman the c3 number means more clearance then the standard bearing clearance. No c is used if it is standard clearance. c2 means less than standard clearance.In this case it is used because chainsaws rely on the oil in the mix to oil them. Hi speed bearings are usually run in a oil bath and some using oil coolers. Greased bearings are usually standard clearance. I could go on all day about what types of bearings are stronger etc. but not today. Looser clearance is also allowed for bearings in hot envirement that can,t be cooled by water or oil. A chainsaw relies on the fan on ignition or starter end also cylinder fins. Allan