are of + noun

[anhnha]

Bellow is a passage from a my slide:
1.“a”, “b”, “cin” are inputs to the adder circuit; “sum” and “carry” are outputs from the circuit.
“a”, “b”, and “sum” are of three bits; “cin” and “carry” are of one bit.

I understand their meanings but what I don't understand is the structure are of + noun.
Can I rewrite the sentence above wihtout "of" like this:
“a”, “b”, and “sum” are three bits; “cin” and “carry” are one bit.
Could you explain more about this structure?
Thank you!

 

[SoothingDave]

I wouldn't use "of" in those sentences, I would write it as you have, except add an "each" or "both" if it is possible that the audience will not understand that "a," "b," and "sum" are each three bits long, not that they together form three bits.