PT-4 power leads are typically used to connect the 18 guage pair of power cable to RG-59 siamese cable to a security cameras DC power plug input.  PT-4 power leads can also be used with pro box style security cameras that do not typically have a DC power plug attached to them.  Box security cameras typically have screw terminals for a positive and negative wire connection.  If you are using plug and play cables, you can attach a PT-4 to the cameras power terminals for a clean connection to your plug and play cables.  PT-4s provide 1 foot of cable and a male connector for CCTV Camera power.  The diameter of the connector is 2.1mm which is the standard size used for plug and play cables.