A clip is the device holds a single fly, a comb is the length of clips - either 5, 7, or 10 (dependant on size) and a plate is the combs riveted on to aluminium mini sheet.
Therefore when we say a 6 inch plate we mean 4 rows of 5s, 5 rows of large 7s, 7 rows of small 7s or 7 rows of 10s mounted onto a small aluminium plate.
I hope that this has explained the terminology for you
Clive Edwards
Author