Micrometer use

Just picked up this Brown and Sharpe no. 55 micrometer set. What is the collar for on the right side. It will rotate one way but not the other. I think the knob on the very end is for getting the measurements since it will click when the moveable side touch the object being measured. Thanks!

This video will explain things much better than I could ever do with just words:
https://www.youtube.com/watch?v=VU23AIlU0Cg

I think it is for locking the barrel in place for when you are making a measurement in a tight or dark place, and you want to make sure that it does not change your reading when you move it to where you can see it and read the numbers.
I'm sure somebody will correct me if I am wrong.

That knob on the end of the barrel is to limit the torque you put on it. Makes for the most accurate measure possible, since you won't be getting it too loose or over cranking it too tight.

Nice find! Yes, the small knob on the right end is for getting consistent measurements every time instead of horsing the mic closed like a C-clamp and deforming both the part and the mic. Learn how to use and calibrate them and they will treat you very well for a long time.

The ring located where the "C" and thimble intersect is a lock to allow secure removal from the measurement to read in the light,
As described below. Jim

Your mic set looks good. Often some of the anvils or standards are missing.

The knurled collar on the right is to lock the spindle to hold a measurement, as someone said. Also as posted, the ratchet (knob) at the end is supposed to slip to give a consistent pressure so the readings are right. They are not fool proof and can slip early or hang up but help until one gets the feel of taking a reading. Many micrometers don't have them and many machinists won't use them even if the mic has one.

There should (and needs to be) be a nut at the extreme left to hold the anvils tight in the frame. Maybe it is there but it doesn't look like it, to me, in your photo. They use the same nut, often round with a knurled outer surface, with all four anvils. You calibrate each anvil to the proper standard (rods in the center) using the adjusting nuts on the inner side of the anvils, locking it with the outer nut before checking with the standard. If that nut is missing you might have trouble finding one, as the threads on the anvils may not be a pitch you find in a hardware store. Some of the B&S 55's had a set screw in the side of the frame where the anvil goes in and there will be a flat spot on the anvil that should line up with it when inserted. That should be just tight enough to keep the anvil from rotating when tightening the outer nut, and will not take the place of the outer nut. Originally there would have been a wrench or two to fit the adjusting nuts as well.

yup the knurled ring in the frame is a lock. The rachet at the end is so you don't use it for a C clamp. I have been told I have a very light touch with a mic as I could feel the stem touch the item being miced lighter than the guy doing the turning in the lathe for me. Since we were both micing it for comparison.

Yes, the nut for the anvil is missing. Thanks for all the information.