Originally Posted by JRems
That amazon one does look like 1/4"x20 thread. For the price I would just get a brass or stainless 1/2" NPT plug and just drill and tap a hole for the 1/4" probe. It would be an easy 10 min job and only add $5 for the plug.
Not sure what kind of plug you meant...
As far as silicone sheet goes I found some on ebay, it's not a shee per say, its 3+ diameter circle 1/8" I think it does look pretty good for what I need as need.