K Type Thermocouple
K type is the most common type of thermocouple. It's inexpensive, accurate, reliable, and has a wide temperature range. The type K is commonly found in nuclear applications because of its relative radiation hardness.

J Type Thermocouple
The Type J is also very common. It has a smaller temperature range and a shorter lifespan at higher temperatures than the Type K. It is equivalent to the Type K in terms of expense and reliability.

T Type Thermocouple
The Type T is a very stable thermocouple and is often used in extremely low temperature applications such as cryogenics or ultra low freezers. It is found in other laboratory environments as well. The Type T has excellent repeatablity between -380F to 392F (-200C to 200C).

E Type Thermocouple
E Type has a stronger signal & higher accuracy than the Type K or Type J at moderate temperature ranges of 1,000F and lower. The type E is also more stable than the type K, which adds to its accuracy. 

Other Considerations for Thermocouple Types

K Type- Known as a general purpose thermocoupole due to its low cost and temperature range. 

J Type- Well suited for oxidizing atmospheres. 

T Type- Well suited for oxidizing atmospheres. 

E Type- In oxidizing or inert atmospheres the operating range is roughly -418F to 1,625F (-250C to 900C).

Which Thermocouple Do You Need?