What is the thread size of the cooling connections on the Conical Fermenter? The thread size of the cooling connections on the Conical Fermenter is 3/8” BSP 19G (metric units) thread.The coupler outer diameter is 16.25mm. Related articles What is the coldest temperature the Grainfather Conical Fermenter can reach? What is the red switch at the base of the G30 boiler? Instructions - How to switch your Original G30 controller from Fahrenheit to Celsius Why is my G30 / G30³ control box not displaying the correct temperature? Technical Specifications - G30³