Lamp Cords with Plugs SPT2 are white, the traditional favorite color for table lamps. Standard insulated 18 gauge wire has 2 parallel copper wires. The positive/hot is smooth, neutral/negative - has ribs. U.L. Listed for table & floor lamps were cord is exposed. Stripped, copper-tipped ends simplify wrapping wire around socket screws. Molded-on plugs are polarized and permanently attached to lamp cord. SPT-2 rating has thicker plastic insulation, see below.
The thickness-rating provides varying degrees of resistance to heat and abrasion. Higher SPT rating numbers provide more resistance to abrasion and more protection from electric shock.