neb: Go to either Bunnnings or M10 to look for 3x2 and type in 70x45 for the search, you get a pile of results for "75x50" (as well as some 150x50). Type in "75x50" for the search and get no results. (And yes, I know about timber sizing, but it's both confusing and non-orthogonal in terms of search results).
Try finding screws on either of them and then your wood requirements will look simple.