I went to HD and that's what they sell there. I looked on the Harbor Freight website and there may be some but so far I couldn't find any
4" with a 7/8 hole.So the thing looks good as new and I'm going to try to get them to let me upgrade to one that properly uses 5/8"/4 inch wheels, to a 4 1/2 inch. Without a receipt, they, or some places, will only give credit for the lowest price charged in the past few months, but I paid the lowest price so that would be fine.
Actually this one would work with 4 1/2 if I could just find a biggere wheel guard. That's why I save parts from junk tools, but I don't have this part.
But I can't get to HF for another week or two. I plan to follow-up then but I can't promise.
They made not sell quality tools but this is the first time they've sold me something I can't get required accesssories for.
BTW, they included one wheel that does fit.
BTW2 I also drilled out a washer to fit over the 5/8" arbor and it does put the wheels at the level of the threads rather than the undercut part, like I planned. So the wheel is now either centered or close, but I can't count on it being centered everytime. I thought of putting some string of the right size in the thread, but how to hold it in place without changing the center of the circle. And I don't want to grind on something, or I won't be able to return the 10 dollar set of 5/8" grinder wheels I bought.