Does a glass candy thermometer, used to measure temp of things like brittle, caramel, etc require tevila? Also, since it is glass can it be used for parve after it was used for milchig?

Shalom, Thank you for your interesting question. In the Hebrew section of this site your very question has already been asked - and Rav Yaakov Ariel answered that he is of the opinion that it does not need tevilah. (I have seen that Rav Avraham Yosef is also of this opinion.) In regards to your question about using it for milk and then meat - the Sephardim are of the opinion that glass never absorbs and therefore may be used for both milk and meat after being cleaned. The Ashkanazim say that for Passover one cannot kosher glass (except in times of great need after getting Rabbinic guidance). In relation to milk and meat there is an argument, with some Ashkanazi Rabbis allowing it and most forbidding it. If you put the thermometer into the pots and pans of food that are, or have been, directly on the fire or in the oven, and foods are hot (more than 45 degrees) then there is even more reason to be strict, and I would advice (if you are Ashkanazi) not to use the same thermometer for both meat and milk. Blessings