Thanks greywolf, it’s good to know the spec. I have an advantage that my brother works for a manufacturer of specialist and custom fasteners, so he has access to a wide range of product. Given that the OE bolt isn’t readily available (I managed to find one dealer with stock in the UK), an alternative is always worth considering. It’s a bit like bearings, same part from a bearing specialist = better availability & better prices. That said, the spec needs to be right.