There are a couple of twists to knowing tubing thickness. 1st is manufacturing inconsistencies. I used to always weigh Columbus SL chain stays because they varied between 140 to 175 grams. I weighted them to find equal weight pairs and also to put lighter ones with lighter riders and so forth. 2nd manufacturing spaces and actual specs are often not the same. For example old SL had .9/.6/.9 wall thicknesses in their top and down tube. While generally correct, they weren't exactly those dimensions. So when looking at a tubing spec chart, it might appear that different brands had the same wall thickness for a particular model but I'm reality were a bit different.