Zip ties and romex wire trains like a champ.
Just to clarify... I think you mean insulated solid core wire. At least, that appears (12AWG or 14AWG) what you appear to be using in your photo. Like this:
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Romex is a cable containing two or more insulated wires enclosed in a plastic or rubberized sheath. Like this:
https://en.wikipedia.org/wiki/Thermoplastic-sheathed_cable#/media/File:Romex_cable.agr.jpg