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Don't know how this got there as the rims are quite new. Looks like a melted welding blob of metal 1mm by 2mm. Can I just use the sandpaper you get with park tools puncture repair glueless patches ?? It's quite a rough grit but any harm in this? I used the same sandpaper little square on my lock-on grips as the plastic inside was sharp and although the paper left some scratches they're on the inside and felt smooth to touch.
Any help much appreciated. Should be good to go as the metal blob is quite hard and will dig into my front pads by the looks of it.
Probably just weld spatter (XC717 is welded not pinned) - there's no harm in cleaning it off, especially if it's on the braking surface.
More accurate help would benefit from a photo though.
Dinged my X717 way back in 2004, still going strong. Tough as old boots, can't see a bit of sandpaper doing any harm.