I wanted to let you guys know of a great product I came across. (I have no affiliation with this company by the way...)
Over at StainlessBrewing.com he is selling these 1/2"OD thermowells. I have had mine just over a week. It is already on it's second fermentation. Here is a picture of mine the day I got it in the mail.
Here is a good picture from this morning showing that the carboy cap seals up NICELY. This was quite active and blew off quite a bit. No krausen came out of the carboy cap around the thermowell.
The sensor probe on the STC-1000 has PLENTY of room and inserts down the I.D. of the tube with no problem at all.