iv got single a/c bearings on my x axis screws at the moment,,,, im having problems with them being to tight on the shaft (my mistake) if i put to much tension on them i wont be able to back them off :( and to take them off the shaft i will damage them. anyway they have been a pain in the jacksy

iv bought two double row A/C's to put in (when i find the time) the only disadvantage iv spotted with the double row is there are fewer balls so lower stress raiting... i cant see this being a problem, they will have a very easy life on a router

if your getting any backlash worth mentioning with double row a/c I'd suspect that some cheeky sod has sold you double row deap grove bearings as angular contacts or they are duds