Your choices are Brickset and LEGO [via pick-a-brick] for official part names/numbers, Rebrickable for official and some fan made names/numbers and BL for fan made numbers/names with some LEGO official names/numbers. Until LEGO started adding part numbers to the moulds very early part numbers are a guess.
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Until LEGO started adding part numbers to the moulds very early part numbers are a guess.