Review on Yeeco + K Type Thermocouple: Ultimate 0~1300℃ Temperature Sensor & Gauge by Scott Koeck

Great price but not suitable for precision furnaces. It reads anything under 2000F or so; which I think is because the pearl is closed by a sleeve. Enough for low temps or something like a forge where +/-25F isn't a big deal. Also, I drilled a hole the same size as the probe and pushed it through 1.5 inches of soft refractory brick insulation. At 2300 F, the back end of the probe felt cold. As long as you drill the hole properly, you shouldn't worry about melting the plastic.