This adapter is used to allow cameras with no hot-shoe - but that do have a PC sync outlet – to use flashes that only feature a hot-shoe connection.
The flash can be mounted unto the adapter, which can then be mounted on the camera's cold shoe, or on a separate flash bracket. The PC end connects to the camera's sync terminal to fire the flash off-camera. This PC sync hot shoe cable compatibles with any model of flash except SONY, Minolta standard flash.
HP-C perfects for CANON hot shoe standard.
HP-N perfects for NIKON hot shoe standard.