These green female receptacles are an easy and quick solution to putting a polarized plug on SPT-1 zipcord. Making your own extension cords or creating custom C7 or C9 based light stringers is a snap using these plugs. Also known in the industry as vampire plugs, these white female receptacles simply slip over the end of a cut cable. Slide on the cover, connect the receptacle to the wire and you are good to go. These plugs come in packs of 50.