Thermocouples are best used for measuring temperatures that can go above 100°C. This is a bare-wire bead-probe which can measure air or surface temperatures. Most inexpensive thermocouples have a vinyl covering which can melt at around 200°C, this one uses a fiberglass braid so it can be used in high temperature measurements such as heaters and ovens. There's a small piece of heat shrink on the end to keep the fiberglass from fraying. If you're using at >250°C temperatures, simply remove it with a small blade.

• K type thermocouple with glass over-braiding
• Good up to 500°C (900 °F)!
• Color-coded wires
• 5 meters long 
• Best used with a thermocouple amplifier such as the MAX31855, AD8495 or MAX31856

We have a handy tutorial which covers thermocouple use including both CircuitPython and Arduino libraries, and example code!