To you and I without a Holley catalog or x-ref, they are just numbers.If you know the list number, you can go here and find out the plate size that corresponds to the number stamped on the airhorn of the carb.
http://www.holley.com/HiOctn/ProdLine/CarbList.pdf
There can be many plates the same size, but different numbers. This is because one plate may be thicker than the other, or have a hole drilled in it or even a slight offset in the mounting holes.
http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSCA/FMSCA.html#Throttle
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Larry
No fast Fords at this time but one fine cruising 96 F350 CC DRW Power Strokin diesel.
And one rusty 64 Fairlane nick-named the Rust Bucket....And sometimes called the Money Pit...
The sounds of a brain dropping into gear.....
"Buzzzzzz.......Click"