These dowels are used as a quick go gage for for GE FDL Master and Art Rods. The individual dowel is inserted into the oil hole and if the dowel is free to travel through the oil passage it indicates a good rod.
If the dowel does not insert completely into the hole that is not necessarily a condemnation of the rod. Casting and drilling discrepancies can affect the oil passage, so the only way to condemn a rod would be to use a T24690 Rod Checking Fixture.