Starrett website has a 3d viewer that will show all parts. is it the 230 P, 230XRL, 230 FL?
If you write to Starrett, they will help also. Starrett used to have available all of the user manuals but they removed them.??
Most mic's are fairly simple in design and number of parts. Don't force anything and use appropriate wrench.
Usually, you remove an end cap and use the allen wrench that comes with the mic or same size.
Be careful with the threads and do not drop anything.
You can also speak to Rene Meyer at Long Island indicator service
for help. Very nice guy and total pro.