Before revision: Ladder line180px|alt=Sketch of nominal 300Ω twin lead|300 Ω twin lead.Parallel wire line comes in three distinct forms: ribbon line or twin lead, a very old version two-conductor ribbon cable, discussed above; window line, a version of ribbon line with periodic holes cut along the insulator's center-line; ladder line or open wire line, a pair of wires periodically spaced apart by insulating "rungs".
After revision: Other similar typesIn addition to Twin-lead, parallel wire line comes in