I use this:
http://www.amazon.com/gp/product/B004XN817Y/?tag=skimlinks_replacement-20
Plugged with this:
http://www.amazon.com/gp/product/B004V3SIR4/?tag=skimlinks_replacement-20 - food safe and can be heated to 400 deg. F
It can make 3 -24 inch or 4 - 18 inch thermowells. Total cost under $30