Check them with those mic standards to see if they're close and record those results. Then turn the thimble opening them until it comes out. Clean the thimble's threads with a mild solvent and a soft bristled toothbrush. A nylon bristled tube brush and more solvent to clean the female threads in the frame.
Air dry, blow them out and peer down there for any foreign boogers. Remove any by brushing again.
Use light oil (sewing machine oil) on the threads. Be frugal with the oil to avoid messes in use and storage. Now check them again with those standards. If you have gauge blocks use those. I have found most mic standards to be inaccurate for real accuracy. Adjustment back to a known value can be accomplished with a mic wrench (which I don't see in the tray). If you don't have or find a mic wrench get ahold of me with your address. I have some you can have. Free.