It depends on the trailer. You measure from the bottom of the coupler with the trailer sitting level. Then measure your drop from the base of the ball. If those numbers match, you are good. A few inches either way shouldn't be a big deal on a 5x8 trailer. I rented a U-haul and had no problems with the stock ball mount. The only thing that sucked was the short draw bar bounces arounds and make a bit of noise.