Okay, by popular request, here's a (slightly blurry) photo of the replacement nut and bolt. Bolt head takes a 5 mm allen wrench. Nut measures 10 mm across flats--same diameter as the cylindrical bolt head. Measuring the hexagonal nut recess in the frame with my cheap slide calipers, I get a flat-to-flat measurement of a little over 9 mm--maybe 9.3 or so, though it's hard to be exact. The 10 mm nut is clearly too big.