For those of who don't know what SPT-1 wire is - it is also known as lamp wire or zip cord, and is commonly used by decorators to build custom lengths of extension cords. It allows for a clean display installation by elimination excess extension cords that can be unsightly. So what are the differences? For some reason this has become a somewhat confusing topic, but really, it's quite simple: They are exactly the same with the exception of the thickness of the insulation covering the wire. Both SPT-1 wire and SPT-2 wire are made using 18 gauge copper wire at their core. The difference is that SPT2 has a thicker insulation around the wire. Thereby making it slightly larger around than SPT1 and giving it the ability to carry a slightly higher electrical load.