Nut sizes

[captonzap]

When I went to return my luggage rack / muffler bracket to its position on the rear of the frame, I didn't like the weathered look of the nuts and bolts, so I went to my local hardware store, which has a fair selection of metric nuts and bolts, and picked up some 8mm hard ware.
When I got home and went to install it, I noticed that there was a size difference in the wrenching flats.
The Hodaka parts were 14 mm, and the new stuff was 13 mm. Both 8 mm dia. and thread pitch.
Was there a different standard back then, or did Hodake use special hardware so that the wrenches supplied in the tool kit could be kept to a minimum and still fit all of the nuts and bolts? Or was the idea that there was more bearing area on the clamping faces?

Wondering, JR