Noel said Hmmm. Well that changes things a bit. That's the first actual photo I've seen of the foot, and I see what you mean. When measuring it, don't just use the ruler on its own. Let's regard the inner vertical surface where it mates to the rack as the normal surface. If you have a length of something straight such as a piece of aluminium angle or steel bar, clamp it with a G-clamp or quick-release clamp to that inner surface and then use an engineers square or setsquare off that. The bar thickness can be easily subtracted later. A sharp pencil to make marks on the foot could help (if you're ok with that, they should rub off). A pencil rubbing on paper, or paper creasing slong eges then drawn over with a ruler can also help to get angled surfaces. I spent some hours at a military museum some years ago taking creasings and rubbings of the fittings on a vehicle there, the staff were very understanding :) Another thing, CAD can make good use of non-perpendicular measurements. So if you're able to measure something across a diagonal or at some odd angle, then please do so. It can be used to triangulate and improve other taken measurements, like a point cloud. Thanks for that, it all helps! Steve.