Brown and Sharpe Caliper Micrometer #250 calibration and disassembly

I am reaching out for some help. I had trouble with this post as it is my first and probably have it in the incorrect thread.

I have a B&S #250 Caliper/Mic that is in pristine condition. I had a very difficult time zeroing out the barrel and thimble. It took a LOT of force to turn the barrel with the small wrench that is supplied with the Mic.

The Mic has about .017 backlash. I would assume that there would be an internal tapered split nut that would adjust the backlash. I have tried to disassemble the Mic but cannot figure out how to disassemble it. I took it to the guy who calibrates the measuring instruments for a large machine shop near me and he cannot take it apart.

I am thinking that there may be some internal corrosion because of the difficulty turning the barrel. When I get it back, I am going to soak it in a penetrant.

But the question is: how is this mic disassembled.

I am attaching a link to a photo off of the web and maybe a thumbnail??

My mic is in NEW AND PRISTINE condition.

BTW I am not a machinist.

https://www.picclickimg.com/d/w1600...ge-Brown-Sharpe-Inside-Micrometer-Caliper.jpg

Boy, that is an old one.

First, I would like to see a closeup photo of the end of the barrel. I wonder if that is some kind of nut there. Perhaps one that requires a special wrench.

Most micrometers will allow you to completely unscrew the moving part, removing it from the main frame. Obviously, due to the movable jaw, this one can not be unscrewed in that direction. Yet, the barrel with the rotating scale on it will prevent it from unscrewing the other way. So there must be some way of separating the two halves of that moving assembly. You say it came with wrenches and you used them to adjust the zero but it was hard to do. I hope you did not bugger it up in dong that as that would lessen it's value to a collector. I suspect that there must be a third place where one of the wrenches can be placed to loosen this adjustment. That may be the key to how it can be disassembled. That same, internal thread that allows adjustment is probably where it is assembled and, therefore, where it can come apart.

A good soak in penetrating OIL is a good idea. That should do no harm. You could even do that in an ultrasonic cleaner to help the penetrating fluid get into the inner mechanism.

Do try to post some closeup photos of that back end and also of all around it. And indicate where you placed the wrenches to adjust it in those photos. A program like Paint allows you to draw arrows or circles on a photo.

PS: I emphasized the word "OIL" above. If you do that soak, DO use an oil so that you are not leaving the internal steel parts unprotected from rust. I would really hate to see a nice piece of machining history like that get messed up.