Ambico Tripod Tripod Head How Can I Determine The Size Of Ball Head For My Tripod?

How can I determine the size of ball head for my tripod? - ambico tripod tripod head

I have a tripod, which is - Ambico V-0554, I think buying a ball, but I can not find a way to measure correctly to the proper setting is possible. Looks like I missed the plate, which attaches the camera for a quick release, and the party has a lever release plate, so that half of the "quick release"

Any help would be great, I am a newcomer on tripods, so they need help.