Sentence Analysis

Hi There,

I recently came accross this sentence:

"I'm not sure what size cable you are using for your termination shunts."

Is Bold words a phrase?

How are the clauses linked ie where is something like relative pronoun or relative adjective or....?

Thanks in advance.

Regards

Muk

(I would also welcome if you can also highlight the any grammitical errors in this qusetion itself.)