the diameters are almost identical. this is so the dist doesn't wobble. the dist is around .00125 smaller than the hole so it takes very little to keep it from going in....if you mark the dist and hole with felt pen then try to stick it in you can see where the high spots are.
my posts keep disaPPEARING SO HERES MY REPLY...the dist has two flanges as you call them. is it stopping on the first one so there is still around 3" of exposed shaft that shoud be inside the engine? is the flange visibly larger? there are two flange sizes, one is small, one is much bigger. if it looks like it is the same size as the hole and it is stopping on the first one then your dist flange might just have a small bur on it. this happens, no prob just find it and sand or file slightly. i have had to do this often. check the hole in the block for burs also.