Where'd you get the parts from? I'm wondering if there is more than one manufacturer of the MKIII isos and they have different threads. I only say that because I've seen different adjustment specs from vendors. There's also a possibility that threads have changed over the years and new adjusters are not compatible with old shafts. That happened with the camshaft threaded hole for example - it was 26 tpi in the old days and new cams are 28 tpi (the factory oil seal guide tool no longer fits!).