Many thanks for all the info on the build and where to source the bits. I have just completed the build and it works just fine. The only things I did differently were 1 I mounted the fan on legs made of 4mm threaded studding fixed to the bottom of the box in order to avoid having bolt heads on the top of the stir plate. 2 I also mounted a speed controller with a red LED on it. Unfortunately at anything other than full speed the the fan emits a loud whine. So I drilled a hole in the case just in front of the LED to make it look a bit more flash. Incidently I used an old Nokia phone charger as the power supply. Without your help it would have taken me much longer if ever at all to build. It's by far the best build that I have seen.