Originally Posted by
stardognine
I just remembered something, some bolt heads have a weird little tang, that sits in a notch, which keeps it from spinning. See if flipping it around might reveal that to you. 🤔
Yeah I thought those nuts had a nub on the backside. It may be intended to fit on the Left side of the bike ('non-drive side" for those who have trouble with right-left)
I have some nuts that are a plain cylinder with M6 thread and a 6 mm allen socket. They came with Gipiemme brake bridges, for recessed brake mounting. Not the normal "top hat" shape of brake nut though, just the cylinder without the flange. Oh right, here's a picture:
They are somewhat precious to me but I will sell one for $10 shipped in the US, if that'll help you. It'll leave me with one brake bridge without a nut, but I'm unlikely to use that bridge anyway...
One disadvantage of this type is the bolt needs to be just the right length. Too long and it fills up the allen socket; too short and you don't have enough threads engaged. A stainless bolt can be trimmed to just the right length without the cut end rusting, if that matters to you.
Dimensions 10 mm diameter, 10 mm long, 6 mm length of threads. Chrome plated.
Mark B in Seattle