Buying A Used Boat In Ontario Taxes When Buying A Used Boat, How Will I Know What Size Trailer Ball I Need For The Trailer?

When buying a used boat, how will i know what size trailer ball I need for the trailer? - buying a used boat in ontario taxes

Will obviously get to choose the boat, although there are standard-sized balls, etc.? And I do not want the wrong size hook. Also, what do I know what an inch "drop" I need to connect it? 2 ", 3"?