Problems Help! Drop Down List with similar name titles

Hey guys...

Im trying to make a list of multi Columns...Such as small example below

NAMES ------ DIAMETER
18KX ------------- 20
20KX ------------- 30
18WX ------------- 50
20VS ------------- 10

So i make a validation Cell for "Names", Then a "=LOOKUP" equation cell to reference the names to the "Diameters"

BUT excel gets confused when i select a "NAME" that is similar to another such as 18KX and 18WX...so it just spits on the first on which is "20"

i can do an IF statement instead of a LOOKUP statement but i have 200 "NAMES" & 200 "DIAMETERS"

how can i do this?!?!?

please help thanks guys!