Just wondered if anyone could help with the sizing of guttering please? I'm aware they isn't a standard size and that they aren't intechangable but wondered when you see 68 mm ,114mm etc., where they are measured from? Do you include the thickness of the material or is it the internal measurement? Sods law, the local merchant only stocks one brand that's a different size. I can't see a logo on the parts that are accessable otherwise I'd have tried surfing to find the manufacturer.