Rear axles

[bmh]

So I was looking through someones stash of rear axles the other day hoping to pick out a couple that were good enough to re-parkerize and use when I noticed something. I thought all rigid frame rear axles were the same. Evidently not, some have a 5/8" thread on the end while others have a 1/2" thread. other than that they are identical in all other respects. they were 11-1/16" long approximatly, had welded on hex heads and the little step inside the head. At first we thought someone buggered the threads and cut new smaller ones, but the work was too perfect for the average garage fix and as it turned out most of them had the smaller threads. I must have looked at 40 or so of these axles with more than half being the smaller thread. So when did they change? All my parts book only list a 5/8 -18 nut from 41-72. Or do these axles fit a different application that I am unaware of? Thanks.

[bmh]

OK, this has been up a week and lots have looked but no one has any thoughts? I guess I'll chalk this one up to PA. once again being the repository for all non-standard bastard H-D parts. I should be an easy guy to spot for a while, I'll be the one crawling around measuring everyone's axle nuts.