I have quite a bit of Spur-type twin-slot shelving. All the DIY and trades places sell it. I always thought it was standard, but the last lot I bought turns out to have vertical slots spaced at 32mm instead of 31.75mm/1.25in. This is enough that the shelf brackets don't line up properly if you try and use the two types of rail side by side.
The retailers don't make it very clear what dimension they're selling or that there are two incompatible flavours. It just seems pointless and unhelpful. I can't imagine what technical benefit there is in moving from exactly 31.75mm, to 32mm - is it dictated by a EU law?