Question

what type of wire is best used with v - knurled drive rolls?
only aluminum
metal cored or flux cored wires
all wires
only hard wires

Explanation:

V - knurled drive rolls are designed to provide better grip. Metal cored or flux cored wires have a structure that allows them to be effectively driven by V - knurled rolls. Aluminum wires are soft and may be damaged by the knurling. Not all wires are suitable as some (like very soft wires) may not work well. And it's not just about hardness as a general "only hard wires" is too vague compared to the specific types of metal cored or flux cored.

Answer:

Metal cored or flux cored wires