Several aftermarket bearing suppliers such as Federal-Mogul, TRW, Clevite, etc. supplied rod and main bearings in .001 and .002 undersizes to allow bearings to compensate for slightly undersize crankshaft journals without regrinding the shaft. It was necessary to measure the journals accurately to be sure they were worn round and not tapered before choosing to use that type of bearing. It was sort of like using .001" different shim thicknesses from side to side on Babbit rods to make a slight alteration in oil clearance.
Jerry

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