Walmart has 6 packs of plastic mason jar lids (with threads) in store for $2.45. I have 3 China bought mini hygrometers that cost me only $5.10 free shipping for all 3. They all compared within 1% of my Accurite hygrometer. Took 5 weeks to arrive from China tho. These only read Celcius, which is no big deal. They have a slight flange which makes it fit nicley on the top of the cutout lid. I'm evaluating how accurate it is. I have a pack of Boost 55% inside the jar, and so far the top meter reads 45% while the inside mini reader already reads 48%. So, I'm still in the evaluation process. I'll give it overnight. It might end up being the meter inside reads more accurately than the meter stuck into the lid.