Thermocouple sheath OD

Thermocouple sheath OD is generally kept at 6mm. What will be the impact on response and accuracy of T/C if sheath thickness is decreased?
Also, what will be the consequences if T/C element thickness is decreased?

GREAT QUESTIONS--for the manufacturers/suppliers of thermocouples. Perhaps you could look at some data sheets for various T/C sheath dimensions to get some idea. usually has some very excellent written materials about temperature measurement and the various methods and types. They sell all manner of temperature and pressure and level sensors and associated equipment and they are well known for their very detailed descriptions of sensors and measurement.

Hope this helps!