Just got a 1994 Royale and getting it tuned up. The threads connecting the extension tube to the whiffle tree shaft seem to need cleaning up. When I go to lower the top, the extension tube doesn't easily back off from the ratchet clutch. The problem is I can't get a good fix on what the thread is. Seems to be about 5/8" diameter, but the 11 pitch doesn't seem to match. I don't want to force it and maybe make a mess of it. I haven't been able to find actual specs anywhere. Anybody know the answer?