Nige,deffo 45-50.when i ordered them off blueflame the guy brought 45-50 and 50-50 link pipes with him(they are about 20miles from me,coz i told him it was a 2000 748r, he wasn't sure on link pipe size).the 50-50 swam on the uprights,the 45-50 were a really tight fit,i had to really wiggle/waggle(tech term!!) them to get them to fit.Have you cleaned inside the link pipes?