Reliable way to find Dell part number without the part in front of you?

Is there a good way to find a searchable part number? Say I need to replace a screen or touchpad in a dell laptop. If I put in the service tag on the Dell support site and look under "Review product specifications" there are codes there for parts but they never match anything on the part I have in front of me. Googling those codes in product specifications doesn't find any part online. Is there something simple I am missing to get searchable part numbers with just the service tag or express code?