I had thought there were two types of needle sizes: mm and numeric. Now, I wonder if there are THREE? two types/categories of numeric? Maybe British and US? I ask because I was starting a little chart to help me and found things like: "6.0 mm(US10)" and "5.0 mm(US8)" but then came across "3.5mm(size 10)" and also "4 mm/No 8" and "3mm/No 11". Thanks.