There's a 1/4" screw going through the quick release plate, and this screws into the camera. The QRP then clips into the tripod head. The head itself is usually threaded 3/8" to screw onto the tripod itself.
Some heads may not have a QRP, and these will just have a 1/4" or 3/8" screw on the head platform.
Screwy or what?
