I have a little Atlas MFC horizontal mill that I found at the dump. It
was pretty grungy, a little rusty, and had a God-awful paint job. So I
stripped it down, cleaned it up, and painted it.

I was reassembling it and did a dry run on the spindle outside its
housing. There was the arbor-side bearing and its covers, the large
back gear, dual pulley, small back gear, spacer, the other bearing &
covers, another spacer, the feed take-off gear, and finally a threaded
collar. It all went pretty well until the threaded collar.

It would only go on about a 1/2 turn. Well, the first thread on the
spindle was a little munged, so I cleaned that up with a file. The
collar still wouldn't go on. But there was a bad spot where a set screw
was tightened down. I cleaned that up and it was no better. Thinking
that maybe a thread just needed to be straightened a little, I tried
force. No good. AYE!! WTF?!?!

Could the threads are different??? The spindle is 7/8 - 14, but the
collar only had 3 threads on it and the pitch was kind of hard to
measure. But it looked like it was 16 pitch!! To be sure, I turned a
7/8 - 16 external thread and the collar fit perfectly!

How could that be? It was fitted together before I stripped it. Well,
now that I mention it, the collar _was_ pretty hard to get off. But a
16 pitch collar on a 14 pitch spindle? Hard to believe.

The fun part was making a 7/8 - 14 collar. First time since 1958 that
I've turned internal threads (or any threads for that matter). It went
good and it fits perfectly. Now you don't have to tell me that I could
have bought one for $6 for MSC. I know that, but what's the fun in it?

Making chips and having a ball,
Bob