I have an F350 with the 3" hitch opening. I also have a Rocky Mounts Backstage swing away two bike hitch rack that is a thing of beauty. The issue is that the supplied bolt from Rocky Mounts is for a 2" receiver and doesn't reach far enough through the 3" hitch when using the Ford 2 step down reducers to get to the two-inch opening. You also cannot use a standard locking pin as the rack has an anti-wobble design that relies on a threaded bolt that snugs things tight.
I then ordered a 3" to 2" adapter that sticks out like four inches, so you have the 2" square that the hitch pin can go through. This contraption should work except for the insane about of slop! This a heavy rack with a swing-away contraption and I flat out hate slop and wiggle :-)
I have been searching for an anti hitch wobble device that is very common for just this type of application, but I cannot find one for the 3" hitch as that's what is wobbling so badly.
Anyone else solve this issue?