Mitutoyo mics tight and threads "lumpy"?

[Matt Irvine]

G'day all,
Today I needed to measure the OD of my rifle barrel, so I pulled out my trusty 25-50 Mitutoyo mic. Upon turning the thimble I had discovered it had become considerably hard to turn, and even when turning it feels real lumpy in the thread. No worries, I'll just back off the split nut, for tightening the threads, and put a drop of tri flow in them. Still no cigar. It's not the spindle brake either.

Does anybody have much experience with these and have any idea what has gone wrong?
The 50-75 and 75-100 are the same. With the 100 being the best of them all. I think that one is just the nut. They are all mitutoyo.

 

[chuckorlando]

If it was fine and is now crunchy you likely have rust or dirt in there. Pull it apart and clean the screw and nut. Oil and put it together. Adjust as needed

 

[Holescreek]

Just for fun, push against the sides of the tube from different directions while turning the thimble and see if it gets easier when pushed from the side.