I can't find the instructions for them, but I think it was 3/8" of tube past the flange. Get the info from moser to be sure. The remaining tube locates the bearing retainer and gives it something to help seal on. I used a metal square to make sure it was square all the way around the tube, grinding and then filing to finish it off. Like TC said, plug the tubes as best you can, the filings will kill your bearings! After four years of draging and driving it on the street no leaks or other problems.