Sure enough, after reading about the 7" dia hub I went to look at all my wheels. The Diamonds have a different stamping than the Bassets and I can see where the 7" support makes sense.
I just last week witnessed a wheel break off a trailer carrying a BobCat. I could hear it squeaking as I came up on it and sure enough, the wheel went flying, it broke the center out just around the outside of the bolt holes.
Summit Racing has steel spacer rings on the website, 7" diameter but only in 5" BC. about $10 each, 1/8" and 1/4" thk.
Gene Winfield "You learn every day"
John