Well, here's an interesting development: my swing arm studs, and the top mount bolts, aren't 10 mm diameter. My machinist discovered this when he measured the broken stud. I have my dial caliper and everything else before me: OEM top bolt, .368" (9.35mm). OEM stud, .373" (9.47mm). Maybe it's meant to be 9mm? But since none of us here has ever come across such a thing, we weren't sure. The thread is a perfect metric 1.25 pitch.
In the end, he decided the prudent thing was to match the three existing fasteners as best he could, so he welded on a 3/8" bolt, which measures .370" (9.40mm) and splits the difference. The only thing is, it's a different thread, but who cares, I suppose.
I ordered 10 mm bushings for my Hagon shocks (based on the recommendation of others here on the forum who have all ordered 10 mm bushings, and of Dave Quinn). The Hagons are loose. Looser than the OEM shocks, as you might imagine. Just for grins, I tried a new 10mm bolt in the 10mm bushings for size, and it's a perfect fit. I measured my OEM shock bushings: they have an ID of .379", or 9.63mm. The new 10mm bushed Hagon bushings have an ID of .393", or 9.98mm. I didn't measure the 10mm bolt, nor did I test fit it in the OEM shock, but the fit on the Hagon was so close, I kind of doubt it would have fit the smaller OEM bushing, but I don't know.
I'm not sure what-all is going on with all these measurements, but in a nutshell, all of my shock mounting hardware is about the same size - only it's not 10mm. It's all about 20 thou smaller than the bushings.
My guy wiggled the fit-together parts a bit before suggesting that I wasn't setting up a race bike, and if it were his, he'd just put it back together and forget about it.
The repair is done, and I think he did the right thing by matching the existing sizes. But now I have to decide about whether to worry about the bushings. Since Dave Quinn only offers 8mm and 10mm bushings, maybe I should follow my guy's advice and just ride the darn thing.
Is a 10mm bushing on a 9.4mm stud too loose? Any thoughts or advice?