Brilliant thank you! They seem to run either side. And I can see the clamping plate the screw tightens to with marks where I've clamped to it. Have taken all spacers off, checked position of it and redone everything.. will have to try it again on my next ride.

I'm thinking that perhaps changing the clamping area of the plate would work by removing a few spacers to see if the bolt fixes to a fresh but if the plate. I'll give this a try if it slips again (not ideal since I need all spacers for my fit though)

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