This set of pot cleaning caps includes US 3/8", metric 8mm and metric 7mm caps.   If you just need one, single cleaning caps are available in my other listings.

They are available in stainless steel, brass or aluminum. 

The 3/8" one is threaded to fit US pots like CTS that have a 3/8" by 32 TPI thread.   The nuts on these pots use a 1/2" wrench.  The 8mm by 0.75 size fits large (24mm) imported pots and some Bourns pots. 8mm pots use an 11mm wrench.  The 7mm fits Alpha and other metric pots that use a 7mm by 0.75 thread.   The nuts on this style pot use a 10mm wrench.

The adapters have a small hole for the tube from your favorite pot cleaning product (I like Caig DeoxIT).  

Here's the process:

• Pull the knob
• Slip an o-ring on the shaft if there's room
• Thread on the cleaning cap
• Put the product tube in the little hole
• Wrap a rag around the bottom (just in case)
  
• Cover the open end with your finger
• Spray

The cleaning solution is directed to the shaft of the pot where it can seep in.   You can turn split shaft pots with a screwdriver through the open end to work in the cleaner.