What is a thread twisted on the upper frame of Nissan sunshine water tank?

Adjust the heating and cooling devices. According to the official information released by Nissan, a thread is screwed on the upper frame of Nissan Sunshine Water Tank to adjust the heater and cooler. The water tank is under the workbench and can't be touched. You need this line to adjust it. Nissan, the full name of Nissan Motor, is a Japanese multinational automobile manufacturer listed on the Tokyo Stock Exchange.