This set of four wires cover sizes below Wallnut 1.
There is not much to choose between them in size so a good choice for most racks would be a 00 and a ½ rather than buying the lot.
They are a cheaper construction than soldered type micro wires, but they need deeper cracks and are not as strong. They have a milled head which protects the wire from damage by 'counter-sinking' it.
The current version has a coloured label to match the colour of the nut.