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Thanks Allted
Yes, sorry. I meant the holes I measured were the ones in the corner mounts that the tubes slide into. It's so tight that I have to pry the 'jaws' of the block open to slide the conduit through. It's not ideal (the bottom and top of the block are at a slight angle to each other, ie. not parallel flat) once the tube goes in. Same goes for the top locks, there is about a 3-4mm gap between the lock and the mounting block (I've put a couple of springs along the screws to fill the gap, which works nicely). Like I said none of this detracts from a brilliant design, it is quite possibly a printing problem (maybe the locks are 'sagging' in the middle when they print ?). The beauty of this 3d printing gig is, I've found, when something doesn't work you can try a different approach easily.
These little niggles aside, it's going to be a very solid machine when its done and I'm eager to get some pictures up.