@swbca can you find any markings on the coupler or trailer hitch mechanism regarding the make or model? Last time I looked Mastercraft was using Phoenix to make their trailers. Phoenix uses UFP mechanicals, the picture you shared of the coupler doesn’t look like the typical UFP A-60 which uses a 2-inch ball. Knowing what coupler you have would rule out the ball size. Also how old is your trailer ball? Might want to check its diameter, they are a wear item should be replaced if their diameter is below specifications. Most of the newer couplers are not adjustable, I’m not sure I would be comfortable with 1/4” of play between the ball and coupler. Glad you ruled out one area of play on the receiver. That can cause damage as well if left unchecked.