I'm replacing the U-joints in my 05 F250 FX4, front flange and mid flange no problem with the 330 U-joints. However on the rear axle flange the 330 is to big , I can't seat both external lock rings , the measurements on the flange from ring groove to ring groove are 4 1/8" (on both the flange and the shaft ) ... the new 330 measures at 4 3/16" ??? I'm lost and confused any help thanks in advance

 

Something to check,
Many times in spite of best efforts, one of the needles in a cap will fall out and get jammed under the cap and prevent full installation.
If this is confirmed to not be the problem, wrong u- joint !